Accessory apparatus, image-capturing apparatus, control method and storage medium storing control program

ABSTRACT

The accessory apparatus includes an accessory communicator providing a notification channel (RTS), a first data communication channel (DCL) and a second data communication channel (DCL). The accessory controller transmits, in a transmission request receiving state of receiving a transmission request from an image-capturing apparatus through the notification channel, accessory data to the image-capturing apparatus through the first data communication channel, and receives camera data transmitted through the second data communication channel from the image-capturing apparatus in response to receiving the accessory data. The accessory controller stops, in the transmission request receiving state and during transmission of the accessory data to the image-capturing apparatus, in response to becoming a non-transmission request receiving state, transmitting the accessory data to the image-capturing apparatus.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 16/850,098,filed Apr. 16, 2020, which is a divisional of application Ser. No.15/468,240, filed Mar. 24, 2017, which issued as U.S. Pat. No.10,674,064 on Jun. 2, 2020, the entire disclosures of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image-capturing apparatus(hereinafter referred to as “a camera body”) and an accessory apparatussuch as an interchangeable lens communicable with each other.

Description of the Related Art

In an accessory-interchangeable camera system including a camera body towhich an accessory apparatus is detachably attachable, the camera bodyand the accessory apparatus communicate with each other for controllingthe accessory apparatus from the camera body and for providing, from theaccessory apparatus to the camera body, data required for controllingthe accessory apparatus.

In particular, when an interchangeable lens is used for capturing amoving image to be recorded or a live-view moving image to be displayed,smooth lens control in synchronization with image-capturing periods isrequired, so that it is necessary to synchronize image-capturing timesin the camera body with control times in the interchangeable lens. Thus,the camera body is required to complete receipt of the data from theinterchangeable lens and transmission of various commands and requeststo the interchangeable lens in one image-capturing period. However, anincrease in amount of the data to be received by the camera body fromthe interchangeable lens and a reduction of the image-capturing period(that is, an increase in a frame rate) require a large data volumecommunication in a shorter time. Japanese Patent Laid-Open No.2010-237514 discloses a camera system having a one-directionalcommunication mode (hereinafter referred to as “a high-speed mode”) anda bidirectional communication mode (hereinafter referred to as “alow-speed mode”). In the high-speed mode, a one-directionalcommunication channel for data transmission from a camera body to aninterchangeable lens and another one-directional communication channelfor data transmission from the interchangeable lens to the camera bodyare used in parallel, and thereby burst communication as continuous datacommunication capable of communicating a large amount of data byfull-duplex communication is performed. On the other hand, in thelow-speed mode, one communication channel is used whose communicationdirection is switched between transmission of a request from one of thecamera body and the interchangeable lens to the other and transmissionof data corresponding to the request from the other to the one.

However, when the camera system disclosed in Japanese Patent Laid-OpenNo. 2010-237514 falls into a situation where performing the continuousdata communication is difficult due to an insufficient processing speedof a microcomputer provided in the interchangeable lens or the camerabody in the high-speed mode, the camera system cannot suspend thetransmission of data, which may make the data communication therebetweenimpossible.

In order to avoid such impossibility of the data communication, it isnecessary to set as a communication standard a sufficiently low datacommunication speed with respect to performances of various possiblemicrocomputers or to reduce the amount of data to be transmitted.However, these methods cannot effectively use the performances ofmicrocomputers provided to the camera body and the interchangeable lens,which makes it impossible to achieve high-speed data communication. Onthe other hand, if a buffer provided to the camera body for storing datatransmitted from the interchangeable lens has an insufficient capacitywith respect to a large amount of data transmitted from theinterchangeable lens in one burst communication, the buffer cannot storethe entire transmitted data.

SUMMARY OF THE INVENTION

The present invention provides an accessory apparatus and animage-capturing apparatus capable of performing smooth and fast largevolume date communication.

The present invention provides as an aspect thereof an accessoryapparatus detachably attachable to an image-capturing apparatus. Theaccessory apparatus includes an accessory communicator configured toprovide, with the image-capturing apparatus, three channels that are anotification channel used for providing a notice from theimage-capturing apparatus to the accessory apparatus, a first datacommunication channel used for transmitting accessory data from theaccessory apparatus to the image-capturing apparatus, and a second datacommunication channel used for transmitting camera data from theimage-capturing apparatus to the accessory apparatus, and an accessorycontroller configured to, in a transmission request receiving state ofreceiving a transmission request as the notice from the image-capturingapparatus through the notification channel, transmit the accessory datain frame units to the image-capturing apparatus through the first datacommunication channel, and to receive the camera data in frame unitstransmitted through the second data communication channel from theimage-capturing apparatus that is configured to transmit the camera datain response to receiving the accessory data in frame units. Theaccessory controller is configured to, in the transmission requestreceiving state and during transmission of the accessory data to theimage-capturing apparatus, in response to becoming a non-transmissionrequest receiving state of not receiving the transmission request fromthe image-capturing apparatus, stop transmitting the accessory data tothe image-capturing apparatus.

The present invention provides as another aspect thereof animage-capturing apparatus to which an accessory apparatus is detachablyattachable. The image-capturing apparatus includes a camera communicatorconfigured to provide, with the accessory apparatus, three channels thatare a notification channel used for providing a notice from theimage-capturing apparatus to the accessory apparatus, a first datacommunication channel used for transmitting accessory data from theaccessory apparatus to the image-capturing apparatus, and a second datacommunication channel used for transmitting camera data from theimage-capturing apparatus to the accessory apparatus, and a cameracontroller configured to become and keep a transmission requestproviding state of providing a transmission request as the notice to theaccessory apparatus through the notification channel to thereby causethe accessory apparatus to transmit the accessory data in frame units tothe image-capturing apparatus through the first data communicationchannel, and, in response to receiving the accessory data in frame unitsfrom the accessory apparatus, transmit the camera data in frame units tothe accessory apparatus through the second data communication channel.The camera controller is configured to become, from the transmissionrequest providing state, a non-transmission request providing state ofnot providing the transmission request to the accessory apparatus tothereby cause the accessory apparatus to stop transmitting the accessorydata to the image-capturing apparatus.

The present invention provides as yet another aspect thereof animage-capturing system including the above accessory and image-capturingapparatuses.

The present invention provides as still another aspect thereof a controlmethod for an accessory apparatus detachably attachable to animage-capturing apparatus. The method includes the step of causing theaccessory apparatus to provide, with the image-capturing apparatus,three channels that are a notification channel used for providing anotice from the image-capturing apparatus to the accessory apparatus, afirst data communication channel used for data transmission from theaccessory apparatus to the image-capturing apparatus, and a second datacommunication channel used for data transmission from theimage-capturing apparatus to the accessory apparatus, the step ofcausing the accessory apparatus, in a transmission request receivingstate of receiving a transmission request as the notice from theimage-capturing apparatus through the notification channel, to transmitthe accessory data in frame units to the image-capturing apparatusthrough the first data communication channel, and the step of causingthe accessory apparatus to receive the camera data in frame unitstransmitted through the second data communication channel from theimage-capturing apparatus that is configured to transmit the camera datain response to receiving the accessory data in frame units. The methodfurther includes the step of causing the accessory apparatus, in thetransmission request receiving state and during transmission of theaccessory data to the image-capturing apparatus, in response to becominga non-transmission request receiving state of not receiving thetransmission request from the image-capturing apparatus, to stoptransmitting the accessory data to the image-capturing apparatus.

The present invention provides as still another aspect thereof a controlmethod for an image-capturing apparatus to which an accessory apparatusis detachably attachable. The method includes the step of causing theimage-capturing apparatus to provide, with the accessory apparatus,three channels that are a notification channel used for providing anotice from the image-capturing apparatus to the accessory apparatus, afirst data communication channel used for transmitting accessory datafrom the accessory apparatus to the image-capturing apparatus, and asecond data communication channel used for transmitting camera data fromthe image-capturing apparatus to the accessory apparatus, the step ofcausing the image-capturing apparatus to become and keep a transmissionrequest providing state of providing a transmission request as thenotice to the accessory apparatus through the notification channel so asto cause the accessory apparatus to transmit the accessory data in frameunits through the first data communication channel, and the step ofcausing the image-capturing apparatus, in response to receiving theaccessory data in frame units, to transmit the camera data in frameunits to the accessory apparatus through the second data communicationchannel. The method further includes the step of causing theimage-capturing apparatus to become, from the transmission requestproviding state, a non-transmission request providing state of notproviding the transmission request to the accessory apparatus to therebycause the accessory apparatus to stop transmitting the accessory data tothe image-capturing apparatus.

The present invention provides as yet still another aspect thereof anaccessory apparatus detachably attachable to an image-capturingapparatus. The accessory apparatus includes an accessory communicatorconfigured to provide, with the image-capturing apparatus, threechannels that are a notification channel used for providing a noticefrom the image-capturing apparatus to the accessory apparatus, a firstdata communication channel used for transmitting accessory data from theaccessory apparatus to the image-capturing apparatus, and a second datacommunication channel used for transmitting camera data from theimage-capturing apparatus to the accessory apparatus, and an accessorycontroller configured to, in response to receiving a transmissionrequest as the notice from the image-capturing apparatus through thenotification channel, transmit the accessory data to the image-capturingapparatus through the first data communication channel and configured toreceive the camera data transmitted from the image-capturing apparatusin response to receiving the accessory data through the second datacommunication channel. The accessory controller is configured to, duringtransmission of the accessory data to the image-capturing apparatus, inresponse to not receiving the transmission request from theimage-capturing apparatus, stop transmitting the accessory data to theimage-capturing apparatus, and configured to, after an elapsed time fromnot receiving the transmission request exceeds a predetermined time, inresponse to receiving the transmission request again, terminatetransmitting the accessory data to the image-capturing apparatus.

The present invention provides as further another aspect thereof animage-capturing apparatus to which an accessory apparatus is detachablyattachable. The image-capturing apparatus includes a camera communicatorconfigured to provide, with the accessory apparatus, three channels thatare a notification channel used for providing a notice from theimage-capturing apparatus to the accessory apparatus, a first datacommunication channel used for transmitting accessory data from theaccessory apparatus to the image-capturing apparatus, and a second datacommunication channel used for transmitting camera data from theimage-capturing apparatus to the accessory apparatus, and a cameracontroller configured to provide a transmission request as the notice tothe accessory apparatus through the notification channel to therebycause the accessory apparatus to transmit the accessory data to theimage-capturing apparatus through the first data communication channeland configured to, in response to receiving the accessory data, transmitthe camera data to the accessory apparatus through the second datacommunication channel. The camera controller is configured to, duringreceipt of the accessory data from the accessory apparatus, stopproviding the transmission request to thereby cause the accessoryapparatus to stop transmitting the accessory data to the image-capturingapparatus, and configured to, after an elapsed time from not providingthe transmission request to the accessory apparatus exceeds apredetermined time, provide the transmission request again to theaccessory apparatus to thereby cause the accessory apparatus toterminate transmitting the accessory data to the image-capturingapparatus.

The present invention provides as yet further another aspect thereof animage-capturing system including the above accessory and image-capturingapparatuses.

The present invention provides as still further another aspect thereof acontrol method for an accessory apparatus detachably attachable to animage-capturing apparatus. The method includes the step of causing theaccessory apparatus to provide, with the image-capturing apparatus,three channels that are a notification channel used for providing anotice from the image-capturing apparatus to the accessory apparatus, afirst data communication channel used for transmitting accessory datafrom the accessory apparatus to the image-capturing apparatus, and asecond data communication channel used for transmitting camera data fromthe image-capturing apparatus to the accessory apparatus, the step ofcausing the accessory apparatus, in response to receiving a transmissionrequest as the notice from the image-capturing apparatus through thenotification channel, to transmit the accessory data to theimage-capturing apparatus through the first data communication channel,and the step of causing the accessory apparatus to receive the cameradata transmitted through the second data communication channel from theimage-capturing apparatus in response to receiving the accessory data.The method further includes the step of causing the accessorycontroller, during transmission of the accessory data to theimage-capturing apparatus, in response to not receiving the transmissionrequest from the image-capturing apparatus, to stop transmitting theaccessory data to the image-capturing apparatus, and the step of causingthe accessory controller, after an elapsed time from not receiving thetransmission request exceeds a predetermined time, in response toreceiving the transmission request again, to terminate transmitting theaccessory data to the image-capturing apparatus.

The present invention provides as yet still further another aspectthereof a control method for an image-capturing apparatus to which anaccessory apparatus is detachably attachable. The method includes thestep of causing the image-capturing apparatus to provide, with theaccessory apparatus, three channels that are a notification channel usedfor providing a notice from the image-capturing apparatus to theaccessory apparatus, a first data communication channel used fortransmitting accessory data from the accessory apparatus to theimage-capturing apparatus, and a second data communication channel usedfor transmitting camera data from the image-capturing apparatus to theaccessory apparatus, the step of causing the image-capturing apparatusto provide a transmission request as the notice to the accessoryapparatus through the notification channel to thereby cause theaccessory apparatus to transmit the accessory data to theimage-capturing apparatus through the first data communication channel,and the step of causing the image-capturing apparatus, in response toreceiving the accessory data, to transmit the camera data to theaccessory apparatus through the second data communication channel. Themethod further includes the step of causing the image-capturingapparatus, during receipt of the accessory data from the accessoryapparatus, to stop providing the transmission request to thereby causethe accessory apparatus to stop transmitting the accessory data to theimage-capturing apparatus, and the step of causing the image-capturingapparatus, after an elapsed time from not providing the transmissionrequest to the accessory apparatus exceeds a predetermined time, toprovide the transmission request again to the accessory apparatus tothereby cause the accessory apparatus to terminate transmitting theaccessory data to the image-capturing apparatus.

Moreover, the present invention provides as another aspect thereof anon-transitory storage medium storing a control program as a computerprogram for causing a computer to execute any one of the above controlmethods.

The present invention provides as further another aspect thereof anon-transitory storage medium storing a computer program for causing acomputer to execute any one of the above control methods.

Further features and aspects of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a lens-interchangeable camerasystem that is Embodiment 1 of the present invention.

FIG. 2 illustrates a communication circuit between a camera body and aninterchangeable lens in a first communication setting in Embodiment 1.

FIG. 3 is a diagram illustrating a configuration of camera and lens datatransceivers in a first communication setting in Embodiment 1.

FIGS. 4A to 4C illustrate waveforms of signals transmitted and receivedbetween the camera body and the interchangeable lens in the firstcommunication setting in Embodiment 1.

FIGS. 5A to 5C illustrate waveforms of signals transmitted and receivedbetween a camera body and an interchangeable lens in a non-BUSY additionmode in a first communication setting in Embodiment 1.

FIG. 6 illustrates a communication circuit between the camera body andthe interchangeable lens in a second communication setting in Embodiment1.

FIG. 7 is a diagram illustrating a configuration of camera and lens datatransceivers in a second communication setting in Embodiment 1.

FIGS. 8A to 8C illustrate waveforms of signals transmitted and receivedbetween the camera body and the interchangeable lens in the secondcommunication setting in Embodiment 1.

FIGS. 9A and 9B illustrate data frames transmitted and received betweenthe camera body and the interchangeable lens in the first communicationsetting in Embodiment 1.

FIG. 10 is a block diagram illustrating a lens-interchangeable camerasystem that is Embodiment 2 of the present invention.

FIG. 11 is a flowchart illustrating a communication process inEmbodiment 2.

FIGS. 12A and 12B illustrate waveforms of signals transmitted andreceived between a camera body and an interchangeable lens in Embodiment2.

FIG. 13 illustrates an example of setting of a predetermined time in alens-interchangeable camera system that is Embodiment 3 of the presentinvention.

FIG. 14 is a flowchart illustrating a communication process inEmbodiment 4 of the present invention.

FIG. 15 is a block diagram illustrating a configuration of a memorycontroller in Embodiment 4.

FIGS. 16A and 16B illustrate waveforms of signals transmitted andreceived between a camera body and an interchangeable lens in Embodiment4.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the accompanied drawings.

Embodiment 1

FIG. 1 illustrates a configuration of an image-capturing system(hereinafter referred to as “a camera system”) including a camera body200 as an image-capturing apparatus and an interchangeable lens 100 asan accessory apparatus that are a first embodiment (Embodiment 1) of thepresent invention.

The camera body 200 and the interchangeable lens 100 transmit controlcommands and internal information to each other via their communicatorsdescribed later.

The communicators are compatible with various communication methods andswitch their communication formats to the same one in synchronizationwith each other depending on types of data to be communicated andpurposes of their communication, which enables selecting an optimumcommunication format for each of various situations.

Configurations of the interchangeable lens 100 and the camera body 200.The interchangeable lens 100 and the camera body 200 are mechanicallyand electrically connected with each other via a mount 300 including acoupling mechanism. The interchangeable lens 100 receives power supplyfrom the camera body 200 via a power source terminal (not illustrated)provided in the mount 300 and supplies, to various actuators and a lensmicrocomputer described later, power sources necessary for theiroperations. The interchangeable lens 100 and the camera body 200communicate with each other via communication terminals (illustrated inFIG. 2 ) provided in the mount 300.

The interchangeable lens 100 includes an image-capturing optical system.The image-capturing optical system includes, from an object (OBJ) side,a field lens 101, a magnification-varying lens 102 for variation ofmagnification, a stop unit 114 for light amount control, animage-stabilizing lens 103 for image blur correction and a focus lens104 for focusing.

The magnification-varying lens 102 and the focus lens 104 arerespectively held by lens holders 105 and 106. The lens holders 105 and106 are guided by guide bars (not illustrated) movably in an opticalaxis direction in which an optical axis (illustrated by a broken line)of the image-capturing optical system extends and are driven in theoptical axis direction respectively by stepping motors 107 and 108. Thestepping motors 107 and 108 rotate in synchronization with drive pulsesand respectively move the magnification-varying lens 102 and the focuslens 104.

The image-stabilizing lens 103 is moved in a direction orthogonal to theoptical axis of the image-capturing optical system to reduce image blurcaused by user's hand jiggling or the like.

The lens microcomputer 111 as an accessory controller controls variousoperations in the interchangeable lens 100. The lens microcomputer 111receives, via a lens communicator 112 (including a lens data transceiver112 b) as an accessory communicator, control commands transmitted fromthe camera body 200 and transmission requests for lens data (accessorydata) output therefrom. The lens microcomputer 111 performs various lenscontrols corresponding to the control commands and transmits lens datacorresponding to the transmission requests via the lens communicator112. The lens microcomputer 111 performs operations relating to thecommunication with the camera body 200 (that is, with a cameramicrocomputer 205 described later) according to a lens communicationcontrol program as a computer program.

This embodiment employs asynchronous serial communication as acommunication method between the lens microcomputer 111 and the cameramicrocomputer 205. The lens microcomputer 111 and the cameramicrocomputer 205 can share error information indicating that anabnormality of the communication therebetween, that is, a communicationerror is generated.

In addition, the lens microcomputer 111 outputs, in response to a zoomcommand and a focus drive command among the control commands, a zoomdrive signal and a focus drive signal to a zoom driver 119 and a focusdriver 120 to cause them to drive the stepping motors 107 and 108,thereby performing a zoom process to control a magnification variationoperation by the magnification-varying lens 102 and an AF (autofocus)process to control a focus operation by the focus lens 104.

The interchangeable lens 100 is provided with a manual focus ring 130that is rotationally operable by a user and a focus encoder 131 fordetecting a rotational operation amount of the manual focus ring 130.The lens microcomputer 111 causes the focus driver 120 to drive thestepping motor 108 by a drive amount corresponding to the rotationaloperation amount of the manual focus ring 130 detected by the focusencoder 131 to drive the focus lens 104, thereby performing MF (manualfocus).

The stop unit 114 includes stop blades 114 a and 114 b. Anopen-and-close state of the stop blades 114 a and 114 b is detected by ahall element 115, and a detection result thereof is input to the lensmicrocomputer 111 through an amplifier 122 and an A/D converter 123. Thelens microcomputer 111 outputs, depending on the input detection resultfrom the A/D converter 123, a stop drive signal to a stop driver 121 soas to cause the stop driver 121 to drive a stop actuator 113, therebycontrolling a light amount control operation of the stop unit 114.

The interchangeable lens 100 further includes a shake sensor (notillustrated and hereinafter referred to as “a gyro sensor”) constitutedby a vibration gyro or the like. The lens microcomputer 111 drives animage-stabilizing actuator 126 constituted by a voice coil motor or thelike through an image-stabilizing driver 125 depending on a shake(angular velocity) detected by the gyro sensor, thereby performing animage-stabilizing process to control the movement of theimage-stabilizing lens 103.

The camera body 200 includes an image sensor 201 constituted by a CCDsensor, a CMOS sensor or the like, an A/D converter 202, a signalprocessor 203, a recorder 204, the camera microcomputer 205 and adisplay unit 206.

The image sensor 201 photoelectrically converts an object image formedby the image-capturing optical system in the interchangeable lens 100 tooutput an image-capturing signal as an analog electrical signal.

The A/D converter 202 converts the analog image-capturing signal fromthe image sensor 201 into a digital image-capturing signal. The signalprocessor 203 performs various image processes on the digitalimage-capturing signal from the A/D converter 202 to produce a videosignal. The signal processor 203 produces, from the video signal, focusinformation indicating a contrast state of the object image (that is, afocus state of the image-capturing optical system) and luminanceinformation indicating an exposure state. The signal processor 203outputs the video signal to the display unit 206. The display unit 206displays the video signal as a live-view image used for checking animage-capturing composition and the focus state. In addition, the signalprocessor 203 outputs the video signal to the recorder 204. The recorder204 records the video signal.

A memory 210 is constituted by, for example, a DDR (Double Data RateSDRAM). The memory 210 stores the digital image-capturing signalobtained using the image sensor 201 and the video signal produced by theimage processor 203 and stores the lens data received from the lensmicrocomputer 111.

The camera microcomputer 205 as a camera controller controls the camerabody 200 in response to inputs from a camera operation unit 207including an image-capturing instructing switch and various settingswitches (not illustrated). The camera microcomputer 205 transmits, inresponse to a user's operation of a zoom switch (not illustrated), thecontrol command relating to the magnification-varying operation of themagnification-varying lens 102 to the lens microcomputer 111 through acamera communicator 208 (including a camera data transceiver 208 b).Moreover, the camera microcomputer 205 transmits, to the lensmicrocomputer 111 through the camera data transceiver 208 b, the controlcommand relating to the light amount control operation of the stop unit114 depending on the luminance information and the control commandrelating to the focusing operation of the focus lens 104 depending onthe focus information. The camera microcomputer 205 performs operationsrelating to the communication with the lens microcomputer 111 accordingto a camera communication control program as a computer program.

Next, with reference to FIG. 2 , description will be made of acommunication circuit constituted between the camera body 200 (cameramicrocomputer 205) and the interchangeable lens 100 (lens microcomputer111) and of the communication performed therebetween. The cameramicrocomputer 205 has a function of managing settings for thecommunication with the lens microcomputer 111 and a function ofproviding notices such as the transmission requests. On the other hand,the lens microcomputer 111 has a function of producing lens data and afunction of transmitting the lens data.

The camera microcomputer 205 includes a camera communication interfacecircuit 208 a, and the lens microcomputer 111 includes a lenscommunication interface circuit 112 a. The camera microcomputer 205(camera data transceiver 208 b) and the lens microcomputer 111 (lensdata transceiver 112 b) communicate with each other through thecommunication terminals (illustrated by three boxes) provided in themount 300 and the camera and lens communication interface circuits 208 aand 112 a. In this embodiment, the camera and lens microcomputers 205and 111 perform three-wire asynchronous serial communication using threechannels. The camera data transceiver 208 b and the camera communicationinterface circuit 208 a constitute the camera communicator 208. The lensdata transceiver 112 b and the lens communication interface circuit 112a constitute the lens communicator 112.

The three channels are a transmission request channel as a notificationchannel, a first data communication channel and a second datacommunication channel. The transmission request channel is used forproviding the notices such as the transmission requests (transmissioninstructions) for the lens data and switch requests (switchinstructions) for communication settings described later, from thecamera microcomputer 205 to the lens microcomputer 111. The provision ofthe notice through the transmission request channel is performed byswitching a signal level (voltage level) on the transmission requestchannel between High as a first level and Low as a second level. Atransmission request signal provided to the transmission request channelis hereinafter referred to as “a request-to-send signal RTS”.

The first data communication channel is used for transmitting the lensdata from the lens microcomputer 111 to the camera microcomputer 205.The lens data transmitted as a signal from the lens microcomputer 111 tothe camera microcomputer 205 through the first data communicationchannel is hereinafter referred to as “a lens data signal DLC”. Thesecond data communication channel is used for transmitting camera datafrom the camera microcomputer 205 to the lens microcomputer 111. Thecamera data transmitted as a signal from the camera microcomputer 205 tothe lens microcomputer 111 through the second data communication channelis hereinafter referred to as “a camera data signal DCL”.

The request-to-send signal RTS is provided from the camera microcomputer205 as a communication master to the lens microcomputer 111 as acommunication slave.

The camera data signal DCL includes various control commands andtransmission request commands transmitted from the camera microcomputer205 to the lens microcomputer 111. The lens data signal DLC includesvarious lens data transmitted from the lens microcomputer 111 to thecamera microcomputer 205.

The camera and lens microcomputers 205 and 111 set their communicationspeed beforehand and perform the communication (transmission andreceipt) at a communication bit rate according to this setting. Thecommunication bit rate indicates a data amount transferable per secondand is expressed with a unit of bps (bits per second). The camera andlens microcomputers 205 and 111 communicate with each other by afull-duplex communication method enabling mutual transmission andreceipt of data.

The communication method between the camera body 200 and theinterchangeable lens 100 may be performed by three-channelclock-synchronous serial communication instead of the three-channelasynchronous serial communication. Furthermore, in a case of performinglarge volume data transmission from the lens microcomputer 111 to thecamera microcomputer 205, the clock-synchronous serial communication maybe switched to the asynchronous serial communication. In this case, thenotification channel may be used as a clock line for providing a clocksignal from the camera microcomputer 205 to the lens microcomputer 111.This enables selectively using the two communication methods, that is,the asynchronous serial communication and the clock-synchronous serialcommunication without adding a new channel.

In the clock-synchronous serial communication using the three channels,a clock signal CLK is provided from the camera microcomputer 205 as acommunication master to the lens microcomputer 111 as a communicationslave through a clock channel. The camera data signal DCL includesvarious control commands and transmission request commands transmittedfrom the camera microcomputer 205 to the lens microcomputer 111.

The lens data signal DLC includes various lens data transmitted from thelens microcomputer 111 to the camera microcomputer 205 insynchronization with the clock signal LCLK. In the clock-synchronousserial communication, the camera and lens microcomputers 205 and 111communicate with each other by a full-duplex communication methodenabling mutual transmission and receipt of data in synchronization withthe clock signal LCLK.

Next, with reference to FIGS. 3 to 5C and FIGS. 9A and 9B, descriptionwill be made of a first communication setting that is one ofcommunication settings between the camera and lens microcomputers 205and 111. FIG. 3 illustrates a configuration of the camera datatransceiver 208 b in the camera microcomputer 205 and the lens datatransceiver 112 b in the lens microcomputer 111. The cameramicrocomputer 205 includes a CPU 205 a as a core of the cameramicrocomputer 205, an RTS controller 301 and a transmission data buffer302 as a camera data buffer constituted by a RAM or the like. The cameramicrocomputer 205 further includes a receipt data buffer 303 constitutedby a RAM or the like and a buffer controller 304 that controls datastoring and data read-out to and from the buffers 302 and 303.

On the other hand, the lens microcomputer 111 includes a CPU 111 a as acore of the lens microcomputer 111, an RTS detector 316 and a receiptdata buffer 311 constituted by a RAM or the like. The cameramicrocomputer 111 further includes a transmission data buffer 312 as anaccessory data buffer constituted by a RAM or the like and a buffercontroller 313 that controls data storing and data read-out to and fromthe buffers 311 and 312.

The camera data signal DCL to be transmitted from the cameramicrocomputer 205 to the lens microcomputer 111 is stored to thetransmission data buffer 302. For example, when the camera data signalDCL of 128 bytes is transmitted, this camera data signal DCL of 128bytes is first stored to the transmission data buffer 302 and then istransmitted to the lens microcomputer 111. The buffer controller 304reads out the camera data signal DCL frame by frame from thetransmission data buffer 302. The read camera data signal DCL of eachframe is converted from a parallel data signal into a serial data signalby the parallel-serial converter 305 and is transmitted in frame units(frame by frame) from the camera microcomputer 205 to the lensmicrocomputer 111 through the second data communication channel. Thecamera data signal DCL transmitted from the camera microcomputer 205 isconverted from the serial data signal into a parallel data signal by theserial-parallel converter 314 in the lens microcomputer 111. The buffercontroller 313 stores the camera data signal DCL converted into theparallel data signal to the receipt data buffer 311.

The lens data signal DLC to be transmitted from the lens microcomputer111 to the camera microcomputer 205 is stored to the transmission databuffer 312. For example, when the lens data signal DLC of 128 bytes istransmitted, this lens data signal DLC of 128 bytes is first stored tothe transmission data buffer 312 and then is transmitted to the cameramicrocomputer 205. The buffer controller 313 reads out the lens datasignal DLC frame by frame from the transmission data buffer 312. Theread lens data signal DLC of each frame is converted from a paralleldata signal into a serial data signal by the parallel-serial converter315 and is transmitted in frame units (frame by frame) from the lensmicrocomputer 111 to the camera microcomputer 205 through the first datacommunication channel.

The lens data signal DLC transmitted from the lens microcomputer 111 isconverted from the serial data signal into a parallel data signal by theserial-parallel converter 306 in the camera microcomputer 205.

The buffer controller 304 stores the lens data signal DLC converted intothe parallel data signal to the receipt data buffer 303. The lens datasignal DLC stored in the receipt data buffer 303 is read out therefromby a DMA controller 307, and the read lens data signal DLC istransferred and stored to the memory 210.

This first communication setting further includes, as described later, acommunication setting (hereinafter referred to as “a BUSY additionmode”) in which a busy frame is added and a communication setting(hereinafter referred to as “a non-BUSY addition mode”) in which thebusy frame is not added. FIGS. 4A to 4C illustrates waveforms of signalstransmitted and received between the camera and lens microcomputers 205and 111 in the first communication setting. An arrangement of proceduresof the signal transmission and receipt is called a communicationprotocol.

FIG. 4A illustrates signal waveforms of one frame as a minimumcommunication unit. The camera data signal DCL and the lens data signalDLC have mutually different parts in their data formats in the oneframe.

First, description will be made of the data format of the lens datasignal DLC. The lens data signal DLC in the one frame includes, as largeparts, a data frame as a first frame and a BUSY frame as a subsequentframe. A signal level of the lens data signal DLC is held at High in anon-transmission state where data transmission is not performed.

The lens microcomputer 111 sets the signal level to Low in one bit timeperiod in order to provide a notice of a start of one frame transmissionof the lens data signal DLC to the camera microcomputer 205. The one bittime period indicating a start of one frame is called “a start bit ST”in this embodiment. That is, one data frame is started from this startbit ST. The start bit ST is provided as a head bit of each one frame ofthe lens data signal DLC.

Next, the lens microcomputer 111 transmits one-byte lens data in 8 bittime period from a subsequent second bit to a ninth bit. The data bitsare arranged in an MSB-first format starting from a highest-order databit D7 and continuing to data bits D6, D5, D4, D3, D2 and D1 in thisorder and ending with a lowest-order data bit D0. Then, the lensmicrocomputer 111 adds one bit parity information (parity bit) PA at atenth bit and sets the signal level of the lens data signal DLC to Highin a time period of a stop bit SP indicating an end of the one frame.Thus, the data frame starting from the start bit SP ends.

Thereafter, as illustrated by “DLC (with BUSY)” in FIG. 4A, the lensmicrocomputer 111 adds the BUSY frame after the stop bit SP. The BUSYframe indicates a time period of a communication standby request BUSY asa notice (hereinafter referred to as “a BUSY notice”) from the lensmicrocomputer 111 to the camera microcomputer 205. The lensmicrocomputer 111 holds the signal level of the lens data signal DLC toLow until terminating the BUSY notice. On the other hand, for a casewhere the BUSY notice is unnecessary to be provided from the lensmicrocomputer 111 to the camera microcomputer 205, as illustrated by“DLC (without BUSY)” in FIG. 4A, a data format is provided that formsone frame without adding the BUSY notice (BUSY frame). That is, the lensmicrocomputer 111 can select as the data format of the lens data signalDLC, depending on a process situation, one to which the BUSY notice isadded and one to which the BUSY notice is not added.

Description will be made of a method of determining the presence andabsence of the BUSY notice; the method is performed by the cameramicrocomputer 205. In FIG. 4A, the signal waveform of “DLC (withoutBUSY)” and the signal waveform of “DLC (with BUSY)” both include bitpositions B1 and B2. The camera microcomputer 205 selects one of thesebit positions B1 and B2 as a BUSY determination position P fordetermining the presence and absence of the BUSY notice. As justdescribed, this embodiment employs a data format that selects the BUSYdetermination position P from the bit positions B1 and B2. This dataformat enables addressing a problem that a process time from thetransmission of the data frame of the lens data signal DLC until thedetermination of the presence of the BUSY notice (the lens data signalDLC is set to Low) is changed depending on a processing performance ofthe lens microcomputer 111. Whether to select the bit position B1 or B2as the BUSY determination position P is set by the communication betweenthe camera and lens microcomputers 205 and 111 before the datacommunication therebetween is performed. The BUSY determination positionP is not necessary to be fixed at the bit position B1 or B2 and may bechanged depending on processing capabilities of the camera and lensmicrocomputers 205 and 111.

FIG. 4B illustrates signal waveforms in a case of performing continuouscommunication in the BUSY addition mode illustrated by “DLC (with BUSY)”in FIG. 4A. The BUSY notice (BUSY frame) from the lens microcomputer 111is provided using the lens data signal DLC through the first datacommunication channel, and a subsequent communication is started afterthe BUSY notice is terminated. In FIG. 4B, CMD1 represents atransmission request command that is transmitted as the camera datasignal DCL from the camera microcomputer 205 to the lens microcomputer111. The lens microcomputer 111 transmits, in response to receiving thistransmission request command CMD1, lens data signals DT1 (DT1 a and DT1b) of two bytes corresponding to the transmission request command CMD1to the camera microcomputer 205.

FIG. 4C illustrates signal waveforms in a case of performingcommunication with switching the communication setting (communicationmode) between the BUSY addition mode and the non-BUSY addition mode. Inan example of FIG. 4C, the communication is first performed in the BUSYaddition mode and then performed in the non-BUSY addition mode. In FIG.4C, CMD2 represents a control command and a transmission request commandthat are transmitted as the camera data signal DCL from the cameramicrocomputer 205 to the lens microcomputer 111. Although FIG. 4Cillustrates a case where the camera microcomputer 205 transmits thecontrol and transmission request commands in one frame, the control andtransmission request commands may be transmitted in mutually separateframes. The lens microcomputer 111 switches, in response to receivingthe control command in the command CMD2, the communication mode from theBUSY addition mode to the non-BUSY addition mode. Then, the lensmicrocomputer 111 transmits, in response to receiving the transmissionrequest command in the command CMD2, lens data signals DT2 (DT2 a to DT2c) of three bytes corresponding to the transmission request command tothe camera microcomputer 205.

Next, description will be made of a data format of the camera datasignal DCL. Specifications of the data format of the camera data signalDCL in one frame are common to those of the lens data signal DLC.However, the addition of the BUSY frame to the camera data signal DCL isprohibited, which is different from the lens data signal DLC.

Next, the communication procedures between the camera and lensmicrocomputers 205 and 111 in the first communication setting will bedescribed. First, the communication procedures in the BUSY addition modewill be described.

The camera microcomputer 205 sets, when an event for starting thecommunication with the lens microcomputer 11 is generated, a signallevel of the request-to-send signal RTS to Low (in other words, assertsthe request-to-send signal RTS) to provide the transmission request tothe lens microcomputer 111. The lens microcomputer 111 having detectedthe transmission request through the assertion (Low) of therequest-to-send signal RTS performs a process to produce the lens dadasignal DLC to be transmitted to the camera microcomputer 205. Then,after a preparation for transmitting the lens data signal DLC iscompleted, the lens microcomputer 111 starts transmitting one frame ofthe lens data signal DLC through the first data communication channel.

The lens microcomputer 111 starts the transmission of the lens datasignal DLC within a time period mutually set by the camera and lensmicrocomputers 205 and 111 after the assertion of the request-to-sendsignal RTS. That is, for the lens microcomputer 111, a strictrestriction is not provided that it is necessary to set the lens data tobe transmitted before a first clock pulse is input thereto in a timeperiod from the assertion of the request-to-send signal RTS to a startof the transmission of the lens data signal DLC.

Next, in response to detecting the start bit ST as a head bit of thedata frame of the lens data signal DLC received from the lensmicrocomputer 111 (that is, in response to a start of receiving the lensdata signal DLC), the camera microcomputer 205 returns the signal levelof the request-to-send signal RTS to High, in other words, negates therequest-to-send signal RTS. The camera microcomputer 205 therebyterminates the transmission request and starts the transmission of thecamera data signal DCL through the second data communication channel.The negation of the request-to-send signal RTS may be performed any oneof before and after the start of the transmission of the camera datasignal DCL. It is only necessary that these negation and transmission beperformed until the receipt of the data frame of the lens data signalDLC is completed.

The lens microcomputer 111 having transmitted the data frame of the lensdata signal DLC adds the BUSY frame to the lens data signal DLC in acase where the BUSY notice is necessary to be provided to the cameramicrocomputer 205. The camera microcomputer 205 monitors the presenceand absence of the BUSY notice and prohibits the assertion of therequest-to-send signal RTS for a subsequent transmission request whilethe BUSY notice is provided. The lens microcomputer 111 executesnecessary processes in a time period where the communication from thecamera microcomputer 205 is prohibited by the BUSY notice and terminatesthe BUSY notice after a subsequent communication preparation iscompleted. The assertion of the request-to-send signal RTS by the cameramicrocomputer 205 for the subsequent transmission request is permittedunder a condition that the BUSY notice is terminated and thetransmission of the data frame of the camera data signal DCL iscompleted.

As just described, in this embodiment, in response to the assertion ofthe request-to-send signal RTS upon the generation of the communicationstarting event in the camera microcomputer 205, the lens microcomputer111 starts transmitting the data frame of the lens data signal DLC tothe camera microcomputer 205. On the other hand, the cameramicrocomputer 205 starts, in response to detecting the start bit ST ofthe lens data signal DLC, transmitting the data frame of the camera datasignal DCL to the lens microcomputer 111. The lens microcomputer 111adds, as needed, the BUSY frame to the data frame of the lens datasignal DLC for providing the BUSY notice and then terminates the BUSYnotice to end one frame communication process. In this communicationprocess, the camera microcomputer 205 and the lens microcomputer 111mutually transmit and receive one byte data.

Next, the communication procedures in the non-BUSY addition mode will bedescribed. The non-BUSY addition mode enables a higher-speed datacommunication as compared with the BUSY addition mode because the BUSYframe is not added.

FIG. 5A illustrates signal waveforms when three frames in which each oneframe is a minimum communication unit are continuously communicated inthe non-BUSY addition mode between the camera and lens microcomputers205 and 111. As described above, in the non-BUSY addition mode, the BUSYnotice is not added to the lens data signal DLC. In the non-BUSYaddition mode, the data format of one frame of the lens data signal DLCis formed only by the data frame, that is, does not include the BUSYframe. Therefore, in the non-BUSY addition mode, the lens microcomputer111 cannot provide the BUSY notice to the camera microcomputer 205. Thisdata format is used for burst communication as continuous communicationin which each interval between frames is shortened so as to transmitrelatively large volume data between the camera microcomputer 205 andthe lens microcomputer 111. That is, the non-BUSY addition mode enableslarge volume data communication at a higher speed.

Furthermore, in the non-BUSY addition mode, each frame of the lens datasignal DLC includes two stop bits SP as final bits, which is more thanthat of each frame of the camera data signal DCL. This difference instop bit number makes a bit length of one frame of the lens data signalDLC longer than that of one frame of the camera data signal DCL. Thereason for the longer bit length will be described later.

FIG. 5B illustrates signal waveforms when the camera microcomputer 205and the lens microcomputer 111 continuously transmit and receive nframes of the camera data signal DCL and n frames of the lens datasignal DLC (that is, when performing the burst communication). Prior tostarting this communication, the camera microcomputer 205 receives anotice indicating n frames as data size (frame number) information fromthe lens microcomputer 111 responding to receiving the camera datasignal DCL of one frame illustrated in FIG. 4A.

The camera microcomputer 205 asserts the request-to-send signal RTS whenan event for starting the communication with the lens microcomputer 111is generated. Thereafter, in the non-BUSY addition mode in which it isunnecessary to negate the request-to-send signal RTS at each frame incontrast to in the BUSY addition mode, the camera microcomputer 205maintains the assertion of the request-to-send signal RTS whileperforming continuous data communication (transmission and receipt) withthe lens microcomputer 111.

The lens microcomputer 111 performs, in response to detecting atransmission request by the assertion of the request-to-send signal RTS,a process for producing the lens data signal DLC to be transmitted tothe camera microcomputer 205. Then, after a preparation for transmittingthe lens data signal DLC is completed, the lens microcomputer 111 startstransmitting a first frame DL1 of the lens data signal DLC to the cameramicrocomputer 205 through the first data communication channel.

The lens microcomputer 111 having transmitted the data frame of thefirst frame of the lens data signal DLC rechecks the request-to-sendsignal RTS. If the request-to-send signal RTS is asserted, the lensmicrocomputer 111 transmits, after the first frame whose transmissionhas been completed, a second frame DL2 of the lens data signal DLC tothe camera microcomputer 205. In this way, while the assertion of therequest-to-send signal RTS is maintained by the camera microcomputer205, the lens microcomputer 111 continuously transmits the n frames DL1to DLn of the lens data signal DLC to the camera microcomputer 205.Then, if the transmission of the n frames indicated in the data sizeinformation is completed, the transmission of the lens data signal DLCis stopped.

The camera microcomputer 205 transmits, in response to detecting thestart bits ST of the frames of the lens data signal DLC from the lensmicrocomputer 111, n frames DC1 to DCn of the camera data signal DCLthrough the second data communication channel. Thus, the assertion ofthe request-to-send signal RST maintained by the camera microcomputer205 enables continuous transmission and receipt of the lens and cameradata signals DLC and DCL whose each frame number corresponds to the datasize information. The camera microcomputer 205 temporarily stores the nframes of the lens data signal DLC continuously received from the lensmicrocomputer 111 to the receipt data buffer 303 through theserial-parallel converter 306. The DMA controller 307 transfers the nframes of the lens data signal DLC stored in the receipt data buffer 303to the memory 210 to finally store these n frames to the memory 210.Therefore, to receive a larger data amount of the lens data signal DLCthan a capacity of the receipt data buffer 303, it is necessary totransfer the lens data signal DLC stored before in the receipt databuffer 303 to the memory 210 so as to secure a free space of the receiptdata buffer 303. However, when the DMA controller 307 cannot access thememory 210 due to a processing situation of the signal processor 203provided in the camera body 200, it is impossible to transfer the nframes of the lens data signal DLC continuously received from the lensmicrocomputer 111 to the memory 210. This results in a lack of the freespace of the receipt data buffer 303, which makes it impossible to storepart of the lens data signal DLC to the memory 210. For example, ifremaining data of the lens data signal DLC in the receipt data buffer303, the remaining data being part of the lens data signal DLC receivedbefore by the camera microcomputer 205 and being not transferred to thememory 210, is overwritten by newly received data, the rewritten data isnot stored to the memory 210. Thus, it is necessary to suspend(temporarily stop) the communication performed between the camera andlens microcomputers 205 and 111 before the data stored in the receiptdata buffer 303 is overwritten.

FIG. 5C illustrates signal waveforms in a case where, during thecontinuous data communication illustrated in FIG. 5B, the cameramicrocomputer 205 or the lens microcomputer 111 instructs a suspensionof the communication. Also in this case, in response to the assertion ofthe request-to-send signal RTS by the camera microcomputer 205, the lensmicrocomputer 111 starts transmitting the lens data signal DLC. Then, inresponse to detecting the start bit ST of the lens data signal DLC, thecamera microcomputer 205 starts transmitting the camera data signal DCL.

In FIG. 5C, T2 w 1 represents a communication suspension time periodwhere the suspension of the communication is instructed by the cameramicrocomputer 205. In response to generation of a communicationsuspension event, the camera microcomputer 205 instructs the lensmicrocomputer 111 to suspend the communication (that is, provides acommunication suspension instruction to the lens microcomputer 111) bytemporarily negating the request-to-send signal RTS. In response todetecting the negation of the request-to-send signal RTS, the lensmicrocomputer 111 suspends transmitting the lens data signal DLC aftercompleting transmitting a frame incompletely transmitted at the time ofdetecting the negation (this last transmitted frame is illustrated asDL6 in FIG. 5C and hereinafter referred to as “a suspension frame”). Inresponse to the transmission suspension of the camera data signal DLC,the camera microcomputer 205 also suspends transmitting the camera datasignal DCL after completing transmitting a frame (illustrated as DC6 inFIG. 5C) thereof corresponding to the suspension frame of the lens datasignal DLC.

Such communication control enables, even when the communicationsuspension instruction is provided during the continuous datacommunication, managing so as to make a transmitted frame number of thelens data signal DLC equal to that of the camera data signal DCL, thatis, so as to synchronize the transmissions of the lens and camera datasignals DLC and DCL. In response to termination of the communicationsuspension event, the camera microcomputer 205 is allowed to assert therequest-to-send signal RTS again to instruct the lens microcomputer 111to restart the communication (that is, provides a communication restartinstruction to the lens microcomputer 111). The lens microcomputer 111restarts, in response to the communication restart instruction,transmitting the lens data signal DLC from a frame subsequent to thesuspension frame (this subsequent frame is illustrated as DL7 in FIG. 5Cand hereinafter referred to as “a restart frame”). Then, in response todetecting the start bit ST of the restart frame, the cameramicrocomputer 205 restarts transmitting the camera data signal DCL froma frame DC7 thereof corresponding to the restart frame of the lens datasignal DLC.

As just described, the camera microcomputer 205 temporarily negates therequest-to-send signal RTS to suspend the communication with the lensmicrocomputer 111. Then, if a received frame number of the lens datasignal DLC at the time of the suspension is less than the frame numberindicated in the data size information, the camera microcomputer 205 isallowed to restart receiving the lens data signal DLC from the lensmicrocomputer 111.

After the end of the communication suspension time period T2 w 1, thelens and camera microcomputers 111 and 205 do not instruct or notify ofa suspension of the communication and perform continuous datatransmission in order from the above-described restart frames DL7, DC7to subsequent frames DL8, DC8 and DL9 and DC9.

Then, in response to occurrence of a communication suspension requestevent when the transmission of the frame DL9 (and receipt of the frameDC9 in the camera microcomputer 205), the lens microcomputer 111notifies the camera microcomputer 205 of a suspension of thecommunication. The notification is performed by not transmitting thelens data signal DLC to the camera microcomputer 205 even though therequest-to-send signal RTS is asserted. In FIG. 5C, T2 w 2 represents acommunication suspension time period where the suspension of thecommunication is instructed by the lens microcomputer 111.

The camera microcomputer 205 always monitors the start bit ST of eachframe of the lens data signal DLC and is programed to stop, in responseto not detecting the start bit ST of a certain frame of the lens datasignal DLC, transmitting a subsequent frame of the camera data signalDCL. Therefore, the camera microcomputer 205 stops, when not receivingthe lens data signal DLC (DL10 in FIG. 5C) from the lens microcomputer111 even though asserting the request-to-send signal RTS, transmittingthe camera data signal DCL (DC10 in FIG. 5C) to the lens microcomputer111, thereby stopping the communication the camera microcomputer 205keeps the assertion of the request-to-send signal RTS during thecommunication suspension time period T2 w 2 instructed by the lensmicrocomputer 111.

Thereafter, in response to termination of the communication suspensionrequest event in the lens microcomputer 111, the lens microcomputer 111restarts transmitting the restart frame DL10 of the lens data signalDLC. The camera microcomputer 205 restarts, in response to detecting thestart bit ST of the restart frame DL10, transmitting the correspondingframe DC10 of the camera data signal DCL.

Next, with reference to FIG. 9A, description will be made of a problemthat may occur when, in the non-BUSY addition mode, a bit rate of thecamera data signal DCL output from the camera microcomputer 205 and thatof the lens data signal DLC output from the lens microcomputer 111 aredifferent from each other. FIG. 9A illustrates a relation of frames ofthe camera and lens data signals DCL and DLC when the camera and lensdata signals DCL and DLC have the same bit length of one frame (dataframe) and the bit rate of the camera data signal DCL is slower thanthat of the lens data signal DLC. Arrows in FIG. 9A illustrates whichstart bit ST of the lens data signal DLC is detected by the cameramicrocomputer 205 and which frame of the camera data signal DCL istransmitted from the camera microcomputer 205 to the lens microcomputer111.

Since the bit rate of the camera data signal DCL is slower than that ofthe lens data signal DLC, delays of the frames of the camera datasignals DCL with respect to the frames of the lens data signal DLC aregradually increased. The camera and lens microcomputers 205 and 111 areperforming continuous data communication, so that gaps(non-communication time periods) are not provided between the frames.Accordingly, accumulation of the delays causes a shift of one frame ormore between the camera and lens data signals DCL and DLC, whichgenerates a difference between the transmitted frame numbers of thecamera and lens data signals DCL and DLC. Furthermore, the above shiftbetween the camera and lens data signals DCL and DLC causes the cameramicrocomputer 205 to skip the start bit ST of one frame of the lens datasignal DLC, which generates a time period corresponding to about oneframe where the camera data signal DCL is not transmitted to the lensmicrocomputer 111. Such a situation makes it difficult to manage thetransmitted frame numbers (communication data amounts) between thecamera and lens microcomputers 205 and 111 and makes the datacommunication therebetween impossible.

Thus, this embodiment provides, as illustrated in FIGS. 5A and 9B, agreater number of the stop bits SP in each frame of the lens data signalDLC than that in each frame of the camera data signal DCL. specifically,each frame of the camera data signal DCL includes one stop bit SP, andon the other hand, each frame of the lens data signal DLC includes twostop bits SP. The data formats of the lens and camera data signals DLCand DCL are mutually the same except for the stop bit number. Thedifference in stop bit number makes the bit number of one frame (dataframe) of the lens data signal DLC greater than that of one frame of thecamera data signal DCL. In other words, the difference in stop bitnumber makes the bit length of one frame of the lens data signal DLClonger than that of one frame of the camera data signal DCL. Thissetting enables, even when the bit rate of the camera data signal DCL isslower than that of the lens data signal DLC, preventing the shifts ofthe frames of the camera data signal DCL with respect to the frames ofthe lens data signal DLC from being accumulated.

When the bit rates of the lens and camera data signals DLC and DCL areequal to each other, the longer bit length of one frame of the lens datasignal DLC than that of one frame of the camera data signal DCL causesthe transmission of the camera data signal DCL to be completed earlierthan that of the lens data signal DLC. Furthermore, even when the bitrate of the camera data signal DCL is slower than that of the lens datasignal DLC due to a bit rate error, one bit as a bit length differenceof one frame is a sufficient margin amount for absorbing a transmissiontime difference between corresponding frames of the camera and lens datasignals DCL and DLC due to the bit rate error.

On the other hand, when the bit rate of the camera data signal DCL isfaster than that of the lens data signal DLC, the above-described frameshift problem does not occur. This is because the setting is made thateach frame of the camera data signal DCL is transmitted in response todetecting the start bit ST in each frame of the lens data signal DLC.Furthermore, even when the bit rates settable in the camera body 200 andthe interchangeable lens 100 are slightly different from each other,increasing the bit number of the stop bits SP in each frame of the lensdata signal DLC enables responding to the difference.

As described above, in the BUSY addition mode in the first communicationsetting, the camera microcomputer 205 can notify the lens microcomputer111 of the suspension of the communication by temporarily negating therequest-to-send signal RTS. Furthermore, the lens microcomputer 111 addsthe BUSY notice (BUSY frame) to the lens data signal DLC to notify thecamera microcomputer 205 of the suspension of the communication. Thesefunctions of the camera and lens microcomputers 205 and 111 enablesmooth and fast data communication therebetween.

On the other hand, in the non-BUSY addition mode in the firstcommunication setting, the camera microcomputer 205 can notify the lensmicrocomputer 111 of the suspension of the communication during theburst communication from the lens microcomputer 111 to the cameramicrocomputer 205 by temporarily negating the request-to-send signalRTS. This function of the camera microcomputers 205 and 111 enablesperforming a large volume data communication at a high speed between thecamera and lens microcomputers 205 and 111 while synchronizing them witheach other.

Next, description will be made of the second communication settingbetween the camera and lens microcomputers 205 and 111. In the secondcommunication setting, as illustrated in FIG. 6 , switchingcommunication directions in the communication interface circuits 208 aand 112 a (that is, switching a communication setting) enables using thesecond data communication channel for lens data transmission from thelens microcomputer 111 to the camera microcomputer 205. Specifically, ina communication circuit for the second data communication channel, inputand output buffers are connected in parallel to the second datacommunication channel such that an input/output direction in the seconddata communication channel is switchable. The input and output buffersare exclusively selectable. The input and output buffers connected inparallel to the second data communication channel are hereinaftercollectively referred to as “an input/output buffer”. In the followingdescription, lens data transmitted from the lens microcomputer 111 tothe camera microcomputer 205 through the second data communicationchannel is referred to as “a second lens data signal DLC2”. In addition,the lens data signal DLC transmitted from the lens microcomputer 111 tothe camera microcomputer 205 with the transmission of the second lensdata signal DLC2 through the first data communication channel isreferred to as “a first lens data signal DLC” in order to distinguishthis first lens data signal DLC from the second lens data signal DLC2.

The second communication setting uses the first and second datacommunication channels for continuous communication (burstcommunication) of the lens data signal to the camera microcomputer 205.This second communication setting enables a large volume datacommunication at a higher speed as compared with the non-BUSY additionmode in the first communication setting. However, when the firstcommunication setting is switched to the second communication setting,it is necessary to avoid collision of the camera data signal DCLtransmitted from the camera microcomputer 205 with the lens data signalDLC2 transmitted from the lens microcomputer 111. Thus, in thisembodiment, the camera and lens microcomputers 205 and 111 perform incooperation with each other a communication setting switching processaccording to a predetermined procedure.

FIG. 7 illustrates a configuration of the camera data transceiver 208 bin the camera microcomputer 205 and the lens data transceiver 112 b inthe lens microcomputer 111. In FIG. 7 , constituent elements common tothose in FIG. 3 are denoted by the same reference numerals as those inFIG. 3 , and their description will be omitted.

The camera data transceiver 208 b includes a communication directionswitcher 1401 that operates a switch 1402 so as to switch theinput/output direction in the second data communication channel to adirection in which the camera microcomputer 205 receives the second lensdata signal DLC2 transmitted from the lens microcomputer 111. Then, inthe camera microcomputer 205, the second lens data signal DLC2 receivedfrom the lens microcomputer 111 through the second data communicationchannel is converted from a serial data signal into a parallel datasignal by the serial-parallel converter 306 and is stored to the receiptdata buffer 303. The receipt data buffer 303 also stores the first lensdata signal DLC received through the first data communication channeland converted from a serial data signal into a parallel data signal bythe parallel-serial converter 306. The second lens data signal DLC2stored in the receipt data buffer 303 is read out therefrom by the DMAcontroller 307, and the read lens data signal DLC is transferred andstored to the memory 210.

The lens data transceiver 112 b includes a communication directionswitcher 1411 that operates a switch 1412 so as to switch theinput/output direction in the second data communication channel to thedirection in which the lens microcomputer 111 transmits the second lensdata signal DLC2 to the camera microcomputer 205. Then, in the lensmicrocomputer 111, the second lens data signal DLC2 stored in thetransmission data buffer 312 is converted from a parallel data signalinto a serial data signal by the parallel-serial converter 315 and istransmitted to the camera microcomputer 205 through the second datacommunication channel. In the lens microcomputer 111, the first lensdata signal DLC stored in the transmission data buffer 312 is convertedfrom a parallel data signal into a serial data signal by theparallel-serial converter 315 and is transmitted to the cameramicrocomputer 205 through the first data communication channel.

Next, description will be made of the procedure in the secondcommunication setting. FIG. 8A illustrates signal waveforms when threeframes each one frame is a minimum communication unit are continuouslycommunicated in the second communication setting between the camera andlens microcomputers 205 and 111. In the second communication setting, asthe non-BUSY addition mode in the first communication setting, eachframe of the first and second lens data signals DLC and DLC2 has a dataformat formed only by the data frame, that is, not including the BUSYframe. That is, the first and second lens data signals DLC and DLC2 havea data format not allowing transmitting the BUSY notice from the lensmicrocomputer 111 to the camera microcomputer 205.

Furthermore, the second communication setting is customized as acommunication setting used only for the lens data transmission from thelens microcomputer 111 to the camera microcomputer 205, that is, cameradata transmission from the camera microcomputer 205 to the lensmicrocomputer 111 is unable to be performed in the second communicationsetting. Moreover, the first and second lens data signals DLC and DLC2have a data format enabling continuous communication without a wait timebetween the stop bit SP of a previous frame and the start bit ST of asubsequent frame.

The data frames of the first and second lens data signals DLC and DLC2have mutually the same data formats in which one frame bit lengthsthereof are equal to each other. This is for a purpose of acommunication management that makes numbers of the transmitted framesequal to each other in a case where the data communication is stopped inits middle. However, relative relations of bit positions in the dataframes of the first and second lens data signals DLC and DLC2 are notnecessarily needed to be identical to each other, that is, a shiftamount of the bit positions between the first and second lens datasignals DLC and DLC2 within one frame length is allowed.

FIG. 8B illustrates signal waveforms when the lens microcomputer 111continuously transmit n frames in total of the first and second lensdata signals DLC and DLC2 to the camera microcomputer 205 in the secondcommunication setting (that is, when performing the burstcommunication).

The camera microcomputer 205 asserts the request-to-send signal RTS whenan event for starting the communication with the lens microcomputer 111is generated. Thereafter, in the second communication setting in whichit is unnecessary to negate the request-to-send signal RTS at eachframe, the camera microcomputer 205 maintains the assertion of therequest-to-send signal RTS while performing continuous datacommunication (transmission and receipt) with the lens microcomputer111.

The lens microcomputer 111 performs, in response to detecting atransmission request by the assertion of the request-to-send signal RTS,a process for producing the first and second lens data signals DLC andDLC2 to be transmitted to the camera microcomputer 205. Then, after apreparation for transmitting the first and second lens data signals DLCand DLC2 is completed, the lens microcomputer 111 starts transmitting afirst frame DL1 of the first lens data signal DLC to the cameramicrocomputer 205 through the first data communication channel.Simultaneously, the lens microcomputer 111 starts transmitting a secondframe DL2 of the second lens data signal DLC2 to the cameramicrocomputer 205 through the second data communication channel.

The lens microcomputer 111 having transmitted the first and secondframes DL1 and DL2 of the first and second lens data signals DLC andDLC2 rechecks the request-to-send signal RTS. If the request-to-sendsignal RTS is asserted, the lens microcomputer 111 transmits, after thefirst and second frames, third and fourth frames DL3 and DL4 of thefirst and second lens data signals DLC and DLC2 to the cameramicrocomputer 205. In this way, while the assertion of therequest-to-send signal RTS is maintained by the camera microcomputer205, the lens microcomputer 111 continuously transmits the n frames intotal of the first and second lens data signals DLC and DLC2 to thecamera microcomputer 205.

Setting the total frame number n of the first and second lens datasignals DLC and DLC2 to an even number makes frame numbers transmittedrespectively through the first and second data communication channelsfrom the lens microcomputer 111 to the camera microcomputer 205 equal toeach other. Although in FIG. 8B the first lens data signal DLCtransmitted through the first data communication channel includes onlyodd frames and the second lens data signal DLC2 transmitted through thesecond data communication channel includes only even frames, the firstand second lens data signals DLC and DLC2 may include other frames.

FIG. 8C illustrates signal waveforms in a case where, during thecontinuous data communication from the first and second lens data signalDLC and DLC2 illustrated in FIG. 8B, the camera microcomputer 205 andthe lens microcomputer 111 each instruct a suspension of thecommunication. In response to the assertion of the request-to-sendsignal RTS by the camera microcomputer 205, the lens microcomputer 111starts transmitting the first and second lens data signals DLC and DLC2.Thereafter, while frames DL11 and DL12 are being transmitted, the cameramicrocomputer 205 instructs the suspension of the communication.

In FIG. 8C, T4 w 1 represents a communication suspension time periodwhere the suspension of the communication is instructed by the cameramicrocomputer 205. In response to generation of a communicationsuspension event, the camera microcomputer 205 instructs the lensmicrocomputer 111 to suspend the communication (that is, provides acommunication suspension instruction to the lens microcomputer 111) bytemporarily negating the request-to-send signal RTS.

In response to detecting the negation of the request-to-send signal RTS,the lens microcomputer 111 suspends transmitting the first and secondlens data signals DLC and DLC2 after completing transmitting the framesDL11 and DL12 incompletely transmitted at the time of detecting thenegation (the frames DL11 and DL12 are hereinafter referred to as“suspension frames”).

In response to termination of the communication suspension event, thecamera microcomputer 205 asserts the request-to-send signal RTS again toinstruct the lens microcomputer 111 to restart the communication (thatis, provides a communication restart instruction to the lensmicrocomputer 111). The lens microcomputer 111 restarts, in response tothe communication restart instruction, transmitting the first and secondlens data signals DLC and DLC2 from frames DL13 and DL14 subsequent tothe suspension frames DL11 and DL12 (the subsequent frames DL13 and DL14are hereinafter referred to as “restart frames”).

The lens microcomputer 111 continuously transmits, to the cameramicrocomputer 205, the restart frames DL13 and DL14, subsequent framesDL15 and DL16 and further subsequent frames DL17 and Dl18 in this order.

Then, when the transmission of the frames DL17 and DL18 is completed anda communication suspension request event is generated in the lensmicrocomputer 111, the lens microcomputer 111 notifies the cameramicrocomputer 205 of a suspension of the communication.

In FIG. 8C, T4 w 2 represents a communication suspension time periodwhere the suspension of the communication is instructed by the lensmicrocomputer 111. The notification of the suspension of thecommunication from the lens microcomputer 111 is performed by nottransmitting the first and second lens data signals DLC and DLC2 fromthe lens microcomputer 111 even though the request-to-send signal RTS isasserted. The camera microcomputer 205 maintains the assertion of therequest-to-send signal RTS during the communication suspension timeperiod T4 w 2 instructed by the lens microcomputer 111. Thereafter, whenthe communication suspension request event is terminated in the lensmicrocomputer 111, the lens microcomputer 111 restarts transmitting, tothe camera microcomputer 205, the first and second lens data signals DLCand DLC2 from their next restart frames DL19 and DL20. Thus, the lensmicrocomputer 111 transmits, to the camera microcomputer 205, remainingframes included in the first and second lens data signals DLC and DLC2and having not been transmitted to the camera microcomputer 205 due tothe suspension of the communication.

As described above, in the second communication setting, the lensmicrocomputer 111 suspends the transmission of the first and second lensdata signals DLC and DLC2 to the camera microcomputer 205 and therebysuspends the communication between the camera and lens microcomputers205 and 111. This function of the lens microcomputer 111 enablesperforming a large volume data communication at a high speed between thecamera and lens microcomputers 205 and 111 while synchronizing them witheach other.

As described above, this embodiment enables, in both the first andsecond communication settings, both the camera and lens microcomputers205 and 111 to instruct each other to suspend and restart thecommunication. Therefore, this embodiment enables performing comminationcontrol depending on processing loads and capacities of receipt databuffers of the camera and lens microcomputers 205 and 111, which enablessmoothly performing a high-speed large volume data communication withoutmaking the communication impossible.

Embodiment 2

Next, description will be made of a second embodiment (Embodiment 2) ofthe present invention. This embodiment forcibly suspends (stops)continuous transmission (burst communication) of the first and secondlens data signals DLC and DLC2 from the lens microcomputer 111 to thecamera microcomputer 205 in the second communication setting describedin Embodiment 1.

As described in Embodiment 1, in the second setting, using first andsecond data communication channels for transmitting the first and secondlens data signals DLC and DLC2 from the lens microcomputer 111 to thecamera microcomputer 205 enables a high-speed large volume datacommunication. However, since the second data communication channel isoriginally provided for transmission of the camera data signal DCL,using the second data communication channel for transmitting the secondlens data signal DLC2 makes it impossible to notify the lensmicrocomputer 111 of instructions such as control commands from thecamera microcomputer 205. Therefore, even when the camera microcomputer111 recognized a communication abnormality during the burstcommunication, the camera microcomputer 205 cannot instruct the lensmicrocomputer 111 to suspend the transmission of the first and secondlens data signals DLC and DLC2. The communication abnormality includesdata corruption due to static electricity and shut-off of thecommunication channels between the camera and lens microcomputers 205and 111 due to user's abrupt detachment of the interchangeable lens 100from the camera body 200.

When such communication abnormality occurs, it is desirable to forciblysuspend the communication promptly. However, instructing the lensmicrocomputer 111 to suspend the communication after the burstcommunication from the lens microcomputer 111 to the cameramicrocomputer 205 in the second communication setting and then thesecond data communication channel is switched to the first communicationsetting for transmitting the camera data signal DCL delays thesuspension of the communication. Thus, this embodiment enables promptlyforcibly suspension of the communication when the communicationabnormality occurs.

FIG. 10 illustrates a camera system of this embodiment including acamera system 200′ and an interchangeable lens 100′. In the camerasystem of this embodiment, constituent elements common to those inEmbodiment 1 (FIG. 1 ) are denoted by the same reference numeral asthose in Embodiment 1 and description thereof is omitted.

In FIG. 10 , the interchangeable lens 100′ includes a timer 114 thatcounts an elapsed time from a time counting start command output fromthe lens microcomputer 111 to a time counting end command therefrom. Thelens microcomputer 111 outputs, in response to a negation of therequest-to-send signal RTS by the camera microcomputer 205, the timecounting start command to the timer 114. Then, the lens microcomputer111 outputs, in response to an assertion of the request-to-send signalRTS, the time counting end command to the timer 114. Thereby, the timer211 provided in the camera body 200′ counts the elapsed time, that is, atime for which the request-to-send signal RTS is negated by the cameramicrocomputer 205 (the time is hereinafter referred to as “a lens RTSnegation time”). The lens RTS negation time is input to the lensmicrocomputer 111.

On the other hand, the camera body 200′ includes a timer 211 that countsan elapsed time from a time counting start command output from thecamera microcomputer 205 to a time counting end command therefrom. Thecamera microcomputer 205 negates the request-to-send signal RTS andsimultaneously outputs time counting start command to the timer 211.Thereby, the timer 211 counts the elapsed time, that is, a time forwhich the camera microcomputer 205 negates the request-to-send signalRTS (the time is hereinafter referred to as “a camera RTS negationtime”). The camera RTS negation time is input to the cameramicrocomputer 205.

With reference to a flow chart of FIG. 11 , description will be made ofa communication control process in this embodiment. The cameramicrocomputer 205 and the lens microcomputer 111 execute this processaccording to a communication control program as a computer program. Thefollowing description will be made of a case of forcibly suspending theburst communication while the second communication setting described inEmbodiment 1 is made. However, the process may be performed for forciblysuspending the communication while the first communication setting ismade. The process is started from a state where the first communicationsetting is made. In FIG. 11 and the following description, “S”represents a step.

At S1101, the camera microcomputer 205 prepares a burst communicationrequest command. The burst communication request command includesinformation necessary for the lens microcomputer 111 to perform theburst communication, such as a communication data amount and a bit ratein the burst communication. Then, at S1102, the camera microcomputer 111transmits, as the camera data signal DCL, the burst communicationrequest command to the lens microcomputer 111 through the second datacommunication channel.

At S1201, the lens microcomputer 111 having received the burstcommunication request command performs a communication preparation thatincludes producing the first and second data signals DLC and DLC2according to the information included in the burst communication requestcommand and switching from the first communication setting to the secondcommunication setting. Then, after the communication preparation iscompleted, the lens microcomputer 111 at S1202 transmits, as the firstcamera data signal DLC, a preparation completion notice to the cameramicrocomputer 205 through the first data communication channel.

The camera microcomputer 205 having received at S1103 the preparationcompletion notice asserts at S1104, in response to a completion of acommunication preparation in the camera microcomputer 205, therequest-to-send signal RTS to provide a transmission request to the lensmicrocomputer 111. The lens microcomputer 111 having received thetransmission request starts at S1203 and S1204 a continuouscommunication (burst communication) of the first and second lens datasignals DLC and DLC2 to the camera microcomputer 205 through the firstand second communication channels.

During this burst communication, the camera microcomputer 205 alwaysmonitors presence and absence of a communication error. The followingdescription will be made of a case where the camera microcomputer 205detects at S1105 the communication error is detected during receivingthe first lens data signal DLC or the second lens data signal DLC2. Thecommunication error can be detected by the presence of an inconsistencybetween the parity information PA added to each frame as described inFIG. 8A and a parity of the received data. Furthermore, thecommunication error includes a case where the stop bit SP cannot becorrectly detected and a case where the communication becomes impossibledue to detachment of the interchangeable lens 100 from the camera body200.

The camera microcomputer 205 having detected the communication errorproceeds to S1106. The camera microcomputer 205 having detected nocommunication error continues receiving the first and second lens datasignals DLC and DLC2.

At S1106, the camera microcomputer 205 provides the time counting startcommand to the timer 211 to cause the timer 211 to start counting thecamera RTS negation time. Then, the camera microcomputer 205 at S1107negates the request-to-send signal RTS in order to instruct the lensmicrocomputer 111 to suspend transmitting the first and second lens datasignals DLC and DLC2.

The lens microcomputer 111 having detected the negation of therequest-to-send signal RTS suspends at S1205 transmitting the first andsecond lens data signals DLC and DC2. Furthermore, the lensmicrocomputer 111 at S1206 provides the time counting start command tothe timer 114 to cause the timer 114 to start counting the lens RTSnegation time.

The lens microcomputer 111 at S1207 determines whether or not the lensRTS negation time counted by the timer 114 exceeds a predetermined timeA. The predetermined time A may be preset as a communication standardbetween the camera and lens microcomputers 205 and 111. Alternatively,the predetermined time A may be provided to the lens microcomputer 111by the transmission of the burst communication request command from thecamera microcomputer 205 to the lens microcomputer 111 at S1102 or bytransmission of the camera data signal DCL subsequent thereto. Aspecific example of the predetermined time A will be described in a nextembodiment (Embodiment 3). If the request-to-send signal RTS is assertedby the camera microcomputer 205 before the lens RTS negation timeexceeds the predetermined time A, the lens microcomputer 111 restartstransmitting the first and second lens data signals DLC and DLC2.

If at S1108 the camera RTS negation time counted by the timer 211exceeds the predetermined time A, the camera microcomputer 205 at S1109asserts the request-to-send signal RTS. The camera microcomputer 205thereby instructs the lens microcomputer 111 to forcibly terminate thetransmission of the first and second lens data signals LC and DLC2. Thelens microcomputer 111 detecting the assertion of the request-to-sendsignal RTS after the lens RTS negation time exceeds the predeterminedtime A determines that the assertion is an instruction of forciblyterminating the transmission of the first and second lens data signalsLC and DLC2. The lens microcomputer 111 at S1208 terminates thetransmission of the first and second lens data signals LC and DLC2 inits middle and at S1209 provides a forcible termination completionnotice to the camera microcomputer 205 by transmitting a notice commandas the first lens data signal DCL.

The camera microcomputer 205 having received the forcible suspensioncompletion notice from the lens microcomputer 111 finishes receiving thefirst and second lens data signals LC and DLC2 from the lensmicrocomputer 111 at S1110. Then, the camera microcomputer 205 switchesthe second data communication channel from a state of allowing receiptof the second lens data signal DLC2 to a state of allowing transmissionof the camera data signal DCL.

FIG. 12A illustrates signal waveforms when, in the second communicationsetting, n frames (DL1 to DLn) in total of the first and second lensdata signals DLC and DLC2 are continuously transmitted from the lensmicrocomputer 111 to the camera microcomputer 205 with the communicationsuspension time period T4 w 1 inserted in the middle of thetransmission. The lens microcomputer 111 starts, in response to theassertion of the request-to-send signal RTS by the camera microcomputer205, transmitting the first and second lens data signals DLC and DLC2.Thereafter, during the transmission of the frames DL11 and DL12 from thelens microcomputer 111, the camera microcomputer 205 temporarily negatesthe request-to-send signal RTS to instruct the lens microcomputer 111 tosuspend the communication. In response to detecting the negation of therequest-to-send signal RTS, the lens microcomputer 111 completes thetransmission of the frames DL11 and DL12 (hereinafter referred to as“suspension frames”) of the first and second lens data signals DLC andDLC2, which are frames in the middle of their transmission at the timeof the negation, and then suspends the transmission of the first andsecond lens data signals DLC and DLC2. From this time, the counting ofthe communication suspension time period T4 w 1, that is, of the cameraand lens RTS negation times is started.

When a communication suspension request event is terminated in thecamera microcomputer 205 before the communication suspension time periodT4 w 1 exceeds the predetermined time A, the camera microcomputer 205asserts again the request-to-send signal RTS to instruct the lensmicrocomputer 111 to restart transmitting the first and second lens datasignals DLC and DLC2. In response to the instruction, the lensmicrocomputer 111 restarts transmitting the first and second lens datasignals DLC and DLC2 from frames DL13 and DL14 thereof subsequent to thesuspension frames DL11 and DL12.

FIG. 12B illustrates waveforms of signals transmitted and receivedbetween the camera and lens microcomputers 205 and 111 when thecommunication suspension time period T4 w 1 described in FI. 12A exceedsthe predetermined time A. When the communication suspension time period(camera RTS negation time) T4 w 1 exceeds the predetermined time A, thecamera microcomputer 205 asserts the request-to-send signal RTS havingbeen negated until this time to instruct the lens microcomputer 111 toforcibly suspend the communication. When detecting the assertion of therequest-to-send signal RTS after the communication suspension timeperiod (lens RTS negation time) T4 w 1 exceeds the predetermined time A,the lens microcomputer 111 determines that the assertion is theinstruction of forcibly terminating the communication from the cameramicrocomputer 205.

In response to this instruction, the lens microcomputer 111 terminates(ends) the transmission of the first and second lens data signals DLCand DLC2 after transmitting the suspension frames DL11 and DL12.

Furthermore, the lens microcomputer 111 notifies the cameramicrocomputer 205 of the forcible termination completion notice (END).The forcible termination completion notice may be provided in one frameor in multiple frames. The lens microcomputer 111 thus does not transmitremaining frames DL13 to DLn of the first and second lens data signalsDLC and DLC2 to the camera microcomputer 205 and clears them.

As described above, in this embodiment, when in the second communicationsetting the communication error occurs during the burst communicationfrom the lens microcomputer 111, the camera microcomputer 205 canpromptly instruct the lens microcomputer 111 to forcibly suspend theburst communication.

Although this embodiment described the case where, when the camera andlens RTS negation times exceed the predetermined time A, the lensmicrocomputer 111 recognizes that the assertion of the request-to-sendsignal RTS is merely the instruction of forcibly terminating the burstcommunication, the lens microcomputer 111 may recognize that theassertion of the request-to-send signal RTS is an instruction ofre-performing the burst communication (that is, of forcibly terminatingit and restarting from its beginning).

Embodiment 3

Next, description will be made of a third embodiment (Embodiment 3) ofthe present invention. This embodiment also forcibly suspends thecontinuous communication (burst communication) of the first and secondlens data signals DLC and DLC2 from the lens microcomputer 111 to thecamera microcomputer 205 in the second communication setting.

As described with reference to FIG. 7 in Embodiment 1, in the secondsetting, the first and second lens data signals DLC and DCL2 stored inthe receipt data buffer 303 are read out from the receipt data buffer303 to be transmitted to the memory 210 by the DMA controller 307. Thisis because the receipt data buffer 303 has an insufficient capacity withrespect to the data amount of the entire frames of the first and secondlens data signals DLC and DCL2. However, the memory 210 is accessed bynot only the camera communicator 208 but also the image processor 203and others illustrated in FIG. 1 , so that accessing competitiontherebetween causes a wait time and an insufficient processing speed. Inthis case, providing no instruction for suspending the burstcommunication from the camera microcomputer 205 to the lensmicrocomputer 111 results in making the burst communication impossible.

FIG. 13 illustrates an example of the predetermined time A until thelens microcomputer 111 instructs the forcible suspension of the burstcommunication from the lens microcomputer 111 to the cameramicrocomputer 205. The predetermined time A is set depending on the dataamount of the burst communication. In this example, when the data amountof the burst communication is equal to or smaller than the capacity ofthe receipt data buffer (Rx_RAM) 303, the predetermined time is set to 0ms. On the other hand, when the data amount of the burst communicationis larger than the capacity of the receipt data buffer (Rx_RAM) 303, thepredetermined time A is set to 20 ms. The predetermined time A may bearbitrarily set depending not only on the capacity of the receipt databuffer 303, but also on a processing performance of the cameramicrocomputer 205. The predetermined time A may be fixed regardless ofthe capacity of the receipt data buffer 303 and others. In addition,table information indicating the predetermined times A corresponding tovarious data amounts of the burst communication may be stored in aninternal memory in the camera microcomputer 205 or the memory 210. Thisconfiguration makes it possible to notify the lens microcomputer 111 ofthe predetermined time A before the burst communication is started.

Moreover, similar table information may be stored in an internal memoryin the lens microcomputer 111 and the lens microcomputer 111 may set thepredetermined time A depending on the data amount transmitted in theburst communication from the lens microcomputer 111 to the cameramicrocomputer 205 before the burst communication is stared. In thiscase, it is unnecessary that the camera microcomputer 205 notify thelens microcomputer 111 of the predetermined time A.

When the predetermined time A is set to 0 ms, the lens microcomputer 111determines that the assertion of the request-to-send signal RTS from thenegation thereof is not an instruction for restarting the communication,but an instruction for forcibly suspending the communication. On theother hand, when the predetermined time A is set to 20 ms, the lensmicrocomputer 111 determines that the assertion of the request-to-sendsignal RTS from the negation thereof within the predetermined time A isan instruction for restarting the communication. However, when therequest-to-send signal RTS is asserted from the negation thereof afterthe predetermined time A elapses, the lens microcomputer 111 determinesthat the assertion is an instruction for forcibly suspending thecommunication.

This embodiment can decrease a time required until the burstcommunication is forcibly suspended in the case where the receipt databuffer 303 has a sufficient capacity with respect to the data amount ofthe burst communication as compared with Embodiment 2. Thus, during theburst communication in the second communication setting, the cameramicrocomputer 205 detecting the communication error can promptlyinstruct the lens microcomputer 111 to forcibly suspend the burstcommunication. Accordingly, the camera microcomputer 205 enables thelens microcomputer 111 to promptly restart the burst communication.

Embodiment 4

Next, description will be made of a fourth embodiment (Embodiment 4) ofthe present invention. In this embodiment, as illustrated in FIG. the15, a camera body 200″ includes a memory controller 212 that controlsthe memory (DDR) 210. In FIG. 15 , the camera communicator 208 includedin the camera microcomputer 205 is illustrated outside the cameracommunicator 208. The camera body 200″ in this embodiment corresponds tothe camera body 200′ further including the memory controller 212, andthe interchangeable lens is identical to the interchangeable lens 200′.

Description will be made of the memory controller 212. In FIG. 15 , eachof bus interfaces (each abbreviated as a bus IF) 506 is a bus interfacemodule having an interface function with a master module that requestsmemory accesses. The master module is a main processor provided in thecamera body 200″ and including the camera microcomputer 205, the signalprocessor 203 and the camera communicator 208. FIG. 15 illustrates aconfiguration connectable with two identical or different types ofbuses.

An arbiter 501 performs arbitration and ordering on the memory accessrequests to the memory 210 received by the bus interfaces 506. A queuebuffer 502 is used as a buffer to which the memory access requestssubjected to the ordering by the arbiter 501 are temporarily stored. Thecamera microcomputer 205 acquires information on a frequency of thememory access requests (hereinafter referred to as “memory accessfrequency”) from the memory access requests stored in the queue buffer502.

A command outputter 503 sequentially takes out the memory accessrequests stored in the queue buffer 502 and performs accesses to thememory 210 depending on contents of the taken memory access requests. Adata interface 504 is an interface for reading out and writing data fromand into the memory 210 depending on the memory access request outputthe command outputter 503.

A data controller 505 takes in, when the memory access request selectedby the arbiter 501 is a command that requests data writing to the memory210, data to be written from the bus interface 506. A data controller505 stores the data to be written until an actual data writing time andoutputs the data to the data interface 504. The data controller 505further outputs, when the memory access request selected by the arbiter501 is a command that requests data reading from the memory 210, dataread out from the memory 210 to the data interface 504.

This embodiment will describe below a forcible suspension of thecommunication by the camera microcomputer 205 that detects thecommunication abnormality in the burst communication from the lensmicrocomputer 111 to the camera microcomputer 205 in the secondcommunication setting in a case where the camera body 200″ includes theabove-described memory controller 212. FIG. 14 is a flow chartillustrating a communication control process performed by the camera andlens microcomputers 205 and 111. The camera and lens microcomputers 205and 111 execute this process according to a communication controlprogram as a computer program.

At S401 in FIG. 14 , the camera microcomputer 205 acquires theinformation on the memory access frequency from the memory controller212 (queue buffer 502). A high memory access frequency means that amemory access request wait time is long. The memory access request waittime is a time period from a time point at which a first memory accessrequest is performed until a time at which the camera communicator 208becomes a state of being able to receive the burst communication fromthe lens microcomputer 111 is long.

Next, at S402, the camera microcomputer 205 determines, using the memoryaccess frequency acquired at S401, whether or not an image-capturingmode currently set in the camera body 200″ is one in which the memoryaccess frequency of the camera communicator 208 is high (thisimage-capturing mode is hereinafter referred to as “a high memory accessfrequency image-capturing mode”). If the current image-capturing mode isthe high memory access frequency image-capturing mode, the cameramicrocomputer 205 proceeds to S403. If the current image-capturing modeis not the high memory access frequency image-capturing mode (that is, alow-memory access frequency image-capturing mode), the cameramicrocomputer 205 proceeds to S404.

At S403, the camera microcomputer 205 sets, in response to the highmemory access frequency, the predetermined time A that is an upper limitof the time (hereinafter referred to as “an RTS negation time”) fornegating the request-to-send signal RTS to suspend the communicationlonger than that set at S404 described later. On the other hand, atS404, the camera microcomputer 205 sets, in response to the low memoryaccess frequency, the predetermined time A shorter than that set atS403. That is, the camera microcomputer 205 sets the predetermined timeA long when the memory access request wait time is long and sets thepredetermined time A short when the memory access request wait time isshort.

Next, at S405, the camera microcomputer 205 transmits the burstcommunication request command as the camera data signal DLC to the lensmicrocomputer 111 through the second data communication channel. Theburst communication request command includes, as described in Embodiment2, the information necessary for the lens microcomputer 111 to performthe burst communication, such as the communication data amount and thebit rate in the burst communication.

The lens microcomputer 111 having received the burst communicationrequest command performs at S406 a communication preparation thatincludes producing the first and second data signals DLC and DLC2according to the information included in the burst communication requestcommand and switching from the first communication setting to the secondcommunication setting. Then, after the communication preparation iscompleted, the lens microcomputer 111 transmits, as the first cameradata signal DLC, a preparation completion notice to the cameramicrocomputer 205 through the first data communication channel.

The camera microcomputer 205 having received the preparation completionnotice asserts at S407, in response to a completion of a communicationpreparation in the camera microcomputer 205, the request-to-send signalRTS to provide a transmission request to the lens microcomputer 111. Thelens microcomputer 111 having received the transmission request starts acontinuous communication (burst communication) of the first and secondlens data signals DLC and DLC2 to the camera microcomputer 205 throughthe first and second communication channels.

During this burst communication, the camera microcomputer 205 alwaysmonitors presence and absence of the communication error. The detectionof the communication error is as described at S1105 in Embodiment 2.When detecting no communication error, the camera microcomputer 205proceeds to S412.

On the other hand, when detecting the communication error, the cameramicrocomputer 205 negates at S408 the request-to-send signal RTS toinstruct the lens microcomputer 111 to suspend the transmission of thefirst and second lens data signals DLC and DLC2. The lens microcomputer111 having detected the negation of the request-to-send signal RTSsuspends transmitting the first and second lens data signals DLC andDLC2. Furthermore, the lens microcomputer 111 provides the time countingstart command described in Embodiment 2 to the timer 114 to cause thetimer 114 to start counting the RTS negation time.

The lens microcomputer 111 at S409 determines whether or not the lensRTS negation time counted by the timer 114 exceeds the predeterminedtime A. If the RTS negation time does not exceed the predetermined timeA, the lens microcomputer 111 proceeds to S410 to determine whether ornot the request-to-send signal RTS is asserted again by the cameramicrocomputer 205. If the request-to-send signal RTS is asserted, thelens microcomputer 111 at S411 restarts the first and second lens datasignals DLC and DLC2. Then, at S412, the lens microcomputer 111determines whether or not the transmission of the whole frames of thefirst and second lens data signals DLC and DLC2 have been completed. Ifthe transmission has been completed, the lens microcomputer 111 endsthis process.

If the request-to-send signal RTS is not asserted at S410, the lensmicrocomputer 111 returns to S409.

If at S409 the RTS negation time counted by the timer 114 exceeds thepredetermined time A, the lens microcomputer 111 proceeds to S413 todetermine whether or not the request-to-send signal RTS is assertedagain by the camera microcomputer 205. If the request-to-send signal RTSis asserted, the lens microcomputer 111 stops at S414 transmitting thefirst and second lens data signals DLC and DLC2. That is, the lensmicrocomputer 111 does not transmit remaining frames of the first andsecond lens data signals DLC and DLC2 to the camera microcomputer 205and clears them.

Then, the lens microcomputer 111 provides a forcible terminationcompletion notice to the camera microcomputer 205 by transmitting anotice command as the first lens data signal DCL. The cameramicrocomputer 205 switches from the second communication setting to thefirst communication setting and then ends this process.

As described above, when the request-to-send signal RTS is assertedagain before the RTS negation time exceeds the predetermined time A, thelens microcomputer 111 determines that the assertion is an instructionof restarting the burst communication and therefore restarts the burstcommunication having been suspended. On the other hand, when therequest-to-send signal RTS is asserted again after the RTS negation timeexceeds the predetermined time A, the lens microcomputer 111 determinesthat the assertion is an instruction of forcibly terminating the burstcommunication and therefore terminates the burst communication.

FIGS. 16A and 16B illustrates signal waveforms when, during thecontinuous transmission of the first and second lens data signals DLCand DLC2 from the lens microcomputer 111 to the camera microcomputer205, a communication suspension time T4 w 1 as the RTS negate time isinserted. The first and second lens data signals DLC and DLC2 originallyinclude, as illustrated in FIG. 16B, n frames (DL1 to DLn) in total.

In FIGS. 16A and 16B, in response to the assertion of therequest-to-send signal RTS by the camera microcomputer 205, the lensmicrocomputer 111 starts transmitting the first and second lens datasignals DLC and DLC2. Thereafter, the camera microcomputer 205temporarily negates the request-to-send signal RTS during thetransmission of the frame DL11 and DL12 from the lens microcomputer 111,thereby instructing the lens microcomputer 111 to suspend thecommunication. In response to detecting the negation of therequest-to-send signal RTS, the lens microcomputer 111 suspendstransmitting the first and second lens data signals DLC and DLC2 aftercompleting transmitting the frames DL11 and DL12 incompletelytransmitted at the time of detecting the negation (the frames DL11 andDL12 are hereinafter referred to as “suspension frames”). From thistime, the counting of the communication suspension time period T4 w 1,that is, of the RTS negation times is started.

FIG. 16A illustrates a case where the image-capturing mode is thehigh-memory access frequency image-capturing mode and thereby thepredetermined time A is set long. On the other hand, FIG. 16Billustrates a case where the image-capturing mode is the low-memoryaccess frequency image-capturing mode and thereby the predetermined timeA is set short.

As illustrated in FIG. 16A, when the camera microcomputer 205 assertsthe request-to-send signal RTS again after the communication suspensiontime period T4 w 1 exceeds the predetermined time A, the lensmicrocomputer 111 determines that the assertion is the instruction offorcibly terminating the communication. In response to this instruction,the lens microcomputer 111 terminates (ends) the transmission of thefirst and second lens data signals DLC and DLC2 after transmitting thesuspension frames DL11 and DL12. Furthermore, the lens microcomputer 111notifies the camera microcomputer 205 of the forcible terminationcompletion notice (END). The forcible termination completion notice maybe provided in one frame or in multiple frames. Thus, the lensmicrocomputer 111 does not transmit remaining frames DL13 to DLn of thefirst and second lens data signals DLC and DLC2 to the cameramicrocomputer 205 and clears them.

On the other hand, as illustrated in FIG. 16B, when the request-to-sendsignal RTS is asserted again by the camera microcomputer 205 before thecommunication suspension time period T4 w 1 exceeds the predeterminedtime A, the lens microcomputer 111 determines that the assertion is aninstruction of restarting transmitting the communication. In response tothe instruction, the lens microcomputer 111 restarts transmitting thefirst and second lens data signals DLC and DLC2 from restart frames DL13and DL14 subsequent to the suspension frames DL11 and DL12.

As described above, this embodiment variably sets the predetermined timeA as the upper limit time depending on difference in memory access waittime due to difference in memory access frequency to the memory 210 thatfinally stores the first and second lens data signals DLC and DLC2.Thus, this embodiment enables setting an optimum upper limit time as thecommunication suspension time for a storing speed at which the first andsecond lens data signals DLC and DLC2 of are stored to the memory 210.Accordingly, after the suspension of the communication in response todetecting the communication error in the camera body 200″, the lensmicrocomputer 111 can promptly determine whether to forcibly terminateor restart the communication.

Although this embodiment described the case where, when the RTS negationtime exceeds the predetermined time A, the lens microcomputer 111recognizes that the assertion of the request-to-send signal RTS ismerely the instruction of forcibly terminating the burst communication,the lens microcomputer 111 may recognize that the assertion of therequest-to-send signal RTS is an instruction of re-performing the burstcommunication (that is, of forcibly terminating it and restarting fromits beginning). Furthermore, when the RTS negation time is likely toexceed the predetermined time A, a priority of an access request fromthe camera microcomputer 205 (camera communicator 208) to the memory 210may be controlled to be increased such that the burst communication fromthe lens microcomputer 111 is completed within the predetermined time A.

Each of the above-described embodiments allows the accessory apparatusand the image-capturing apparatus to suspend or terminate datatransmission from each other, which enables a smooth and high-speedlarge volume data communication between the accessory apparatus and theimage-capturing apparatus.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-073360, filed on Mar. 31, 2016, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An accessory apparatus detachably attachable toan image-capturing apparatus, the accessory apparatus comprising: anaccessory controller configured to control communication between theaccessory apparatus and the image-capturing apparatus, wherein theaccessory controller is configured to, in response to maintaining, aftera signal level of a first channel connected via a first terminal changesfrom a first signal level to a second signal level, the signal level ofthe first channel at the second level, control the communication withthe image-capturing apparatus via a second channel connected via asecond terminal and a third channel connected via a third terminal. 2.The accessory apparatus according to claim 1, wherein the accessorycontroller is configured to transmit accessory data of a plurality offrames via the second channel as the communication performed in responseto the signal level of the first channel being maintained at the secondsignal level.
 3. The accessory apparatus according to claim 2, whereineach frame includes a start bit, 8 bit data, and a stop bit.
 4. Theaccessory apparatus according to claim 1, wherein the accessorycontroller is configured to stop transmitting accessory data in responseto the signal level of the first channel being changed from the secondsignal level to the first signal level.
 5. The accessory apparatusaccording to claim 4, wherein the accessory controller is configured to,in a case where the signal level of the first channel has changed fromthe second signal level to the first signal level in a state wheretransmission of accessory data for a certain frame is incomplete, stoptransmitting accessory data to the image-capturing apparatus after thetransmission of the accessory data for the certain frame is complete. 6.The accessory apparatus according to claim 1, wherein the accessorycontroller is configured to transmit accessory data via the secondchannel and receive camera data via the third channel as thecommunication performed in response to the signal level of the firstchannel being maintained at the second signal level.
 7. The accessoryapparatus according to claim 1, wherein the accessory controller isconfigured to transmit accessory data via the second channel and receivecamera data via the third channel in a response to the transmission asthe communication performed in response to the signal level of the firstchannel being maintained at the second signal level.
 8. The accessoryapparatus according to claim 1, wherein the accessory controller isconfigured to stop receiving camera data via the third channel in aresponse to transmission of accessory data via the second channel beingstopped in a case where the signal level of the first channel ismaintained at the second signal level.
 9. The accessory apparatusaccording to claim 1, wherein the accessory controller is configured totransmit accessory data via the second and third channels as thecommunication performed in response to the signal level of the firstchannel being maintained at the second signal level.
 10. The accessoryapparatus according to claim 1, wherein the accessory controller isconfigured to stop transmitting accessory data via the second and thirdchannels in response to elapse of a predetermined time after the signallevel of the first channel has changed from the second signal level tothe first signal level.
 11. The accessory apparatus according to claim1, wherein the accessory controller is configured to transmitinformation on data size of accessory data, and wherein the accessorycontroller is configured to transmit the accessory data of the data sizeindicated by the information in a first mode in which the communicationwith the image-capturing apparatus is performed via the second channeland the third channel in a response to the signal level of the firstchannel being maintained at the second signal level after the signallevel of the first channel has changed from the first signal level tothe second signal level.
 12. The accessory apparatus according to claim11, wherein the information on the data size of the accessory dataindicates the number of frames transmitted as the data size.
 13. Theaccessory apparatus according to claim 11, wherein the accessorycontroller is configured to stop transmitting the accessory data in aresponse to the signal level of the first channel being changed from thesecond signal level to the first signal level in a case wheretransmission of the accessory data of the data size indicated by theinformation is incomplete in the first mode, and resume the transmissionin a response to the signal level of the first channel being changedfrom the first signal level to the second signal level after stoppingthe transmission.
 14. The accessory apparatus according to claim 1,wherein the accessory controller has a second mode different from afirst mode in which the communication with the image-capturing apparatusis performed via the second channel and the third channel in a responseto the signal level of the first channel being maintained at the secondsignal level after the signal level of the first channel has changedfrom the first signal level to the second signal level, and wherein theaccessory controller is configured to perform the communication with theimage-capturing apparatus via the second channel and the third channelin the second mode in a response to the signal level of the firstchannel being changed from the first signal level to the second signallevel.
 15. The accessory apparatus according to claim 14, wherein theaccessory controller is configured to transmit accessory data of oneframe via the second channel as the communication performed in aresponse to the signal level of the first channel being changed from thefirst signal level to the second signal level in the second mode. 16.The accessory apparatus according to claim 14, wherein the accessorycontroller is configured to transmit information on data size ofaccessory data in the second mode.
 17. The accessory apparatus accordingto claim 1, wherein the accessory controller is configured to performthe communication with the image-capturing apparatus via the secondchannel and the third channel in a response to the signal level of thefirst channel being changed from the first signal level to the secondsignal level in a second mode.
 18. The accessory apparatus according toclaim 1, wherein the accessory controller is configured to transmitinformation on data size of accessory data, and wherein the accessorycontroller is configured to, in a case where the signal level of thefirst channel has changed from the second signal level to the firstsignal level in a state where transmission of accessory data for acertain frame is incomplete, stop transmitting accessory data after thetransmission of the accessory data for the certain frame is completeeven if data size of transmitted accessory data is smaller than the datasize indicated by the information.
 19. The accessory apparatus accordingto claim 1, wherein the accessory controller is configured to transmitaccessory data via the second channel in a response to the signal levelof the first channel being maintained at the second signal level afterthe signal level of the first channel has changed from the first signallevel to the second signal level, and receive, via the third channel,camera data transmitted from the image-capturing apparatus in a responseto the transmission of the accessory data via the second channel in aresponse to the signal level of the first channel being maintained atthe second signal level after the signal level of the first channel haschanged from the first signal level to the second signal level.
 20. Theaccessory apparatus according to claim 1, wherein the accessoryapparatus is a lens apparatus.
 21. The accessory apparatus according toclaim 1, wherein the first terminal, the second terminal, and the thirdterminal are different from one another.
 22. An image-capturingapparatus to which an accessory apparatus is detachable attachable, theimage-capturing apparatus comprising: a camera controller configured tocontrol communication between the image-capturing apparatus and theaccessory apparatus, wherein the camera controller is configured to, inresponse to maintaining, after a signal level of a first channelconnected via a first terminal changes from a first signal level to asecond signal level, the signal level of the first channel at the secondlevel, control the communication with the accessory apparatus via asecond channel connected via a second terminal and a third channelconnected via a third terminal.
 23. The image-capturing apparatusaccording to claim 22, wherein the camera controller is configured toreceive accessory data of a plurality of frames via the second channelas the communication performed in a response to the signal level of thefirst channel being maintained at the second signal level.
 24. Theimage-capturing apparatus according to claim 23, wherein each frameincludes a start bit, 8 bit data, and a stop bit.
 25. Theimage-capturing apparatus according to claim 22, wherein the cameracontroller is configured to stop receiving accessory data in a responseto the signal level of the first channel being changed from the secondsignal level to the first signal level.
 26. The image-capturingapparatus according to claim 22, wherein the camera controller isconfigured to, in a case where the signal level of the first channel haschanged from the second signal level to the first signal level in astate where transmission of accessory data for a certain frame isincomplete, stop receiving accessory data after the transmission of theaccessory data for the certain frame is complete.
 27. Theimage-capturing apparatus according to claim 22, wherein the cameracontroller is configured to receive accessory data via the secondchannel and transmit camera data via the third channel as thecommunication performed in a response to the signal level of the firstchannel being maintained at the second signal level.
 28. Theimage-capturing apparatus according to claim 22, wherein the cameracontroller is configured to receive accessory data via the secondchannel and transmit camera data via the third channel in a response tothe transmission as the communication performed in response to thesignal level of the first channel being maintained at the second signallevel.
 29. The image-capturing apparatus according to claim 22, whereinthe camera controller is configured to stop transmitting camera data viathe third channel in a response to reception of accessory data via thesecond channel being stopped in a case where the signal level of thefirst channel is maintained at the second signal level.
 30. Theimage-capturing apparatus according to claim 22, wherein the cameracontroller is configured to receive accessory data via the second andthird channels as the communication performed in a response to thesignal level of the first channel being maintained at the second signallevel.
 31. The image-capturing apparatus according to claim 22, whereinthe camera controller is configured to stop receiving accessory data viathe second and third channels in response to elapse of a predeterminedtime after the signal level of the first channel has changed from thesecond signal level to the first signal level.
 32. The image-capturingapparatus according to claim 22, wherein the camera controller isconfigured to receive information on data size of accessory data, andwherein the camera controller is configured to receive the accessorydata of the data size indicated by the information in a first mode inwhich the communication with the accessory apparatus is performed viathe second channel and the third channel in a response to the signallevel of the first channel being maintained at the second signal levelafter the signal level of the first channel has changed from the firstsignal level to the second signal level.
 33. The image-capturingapparatus according to claim 32, wherein the information on the datasize of the accessory data indicates the number of frames received asthe data size.
 34. The image-capturing apparatus according to claim 32,wherein the camera controller is configured to stop receiving theaccessory data in a response to the signal level of the first channelbeing changed from the second signal level to the first signal level ina case where transmission of the accessory data of the data sizeindicated by the information is incomplete in the first mode, and resumethe reception in a response to the signal level of the first channelbeing changed from the first signal level to the second signal levelafter stopping the reception.
 35. The image-capturing apparatusaccording to claim 22, wherein the camera controller has a second modedifferent from a first mode in which the communication with theaccessory apparatus is performed via the second channel and the thirdchannel in a response to the signal level of the first channel beingmaintained at the second signal level after the signal level of thefirst channel has changed from the first signal level to the secondsignal level, and wherein the camera controller is configured to performthe communication with the accessory apparatus via the second channeland the third channel in the second mode in a response to the signallevel of the first channel being changed from the first signal level tothe second signal level.
 36. The image-capturing apparatus according toclaim 35, wherein the camera controller is configured to receiveaccessory data of one frame via the second channel as the communicationperformed in a response to the signal level of the first channel beingchanged from the first signal level to the second signal level in thesecond mode.
 37. The image-capturing apparatus according to claim 35,wherein the camera controller is configured to transmit information ondata size of accessory data in the second mode.
 38. The image-capturingapparatus according to claim 22, wherein the camera controller isconfigured to perform the communication with the accessory apparatus viathe second channel and the third channel in a response to the signallevel of the first channel being changed from the first signal level tothe second signal level in a second mode.
 39. The image-capturingapparatus according to claim 22, wherein the camera controller isconfigured to receive information on data size of accessory data, andwherein the camera controller is configured to, in a case where thesignal level of the first channel has changed from the second signallevel to the first signal level in a state where reception of accessorydata for a certain frame is incomplete, stop receiving accessory dataafter the reception of the accessory data for the certain frame iscomplete even if data size of received accessory data is smaller thanthe data size indicated by the information.
 40. The image-capturingapparatus according to claim 22, wherein the camera controller isconfigured to receive accessory data via the second channel in aresponse to the signal level of the first channel being maintained atthe second signal level after the signal level of the first channel haschanged from the first signal level to the second signal level, andtransmit, via the third channel, camera data transmitted in a responseto the reception of the accessory data via the second channel in aresponse to the signal level of the first channel being maintained atthe second signal level after the signal level of the first channel haschanged from the first signal level to the second signal level.
 41. Theimage-capturing apparatus according to claim 22, wherein the accessoryapparatus is a lens apparatus.
 42. The image-capturing apparatusaccording to claim 22, wherein the first terminal, the second terminal,and the third terminal are different from one another.
 43. A controlmethod for controlling communication between an accessory apparatus andan image-capturing apparatus in the accessory apparatus detachablyattachable to the image-capturing apparatus, the control methodcomprising: the step of controlling, in response to maintaining, after asignal level of a first channel connected via a first terminal changesfrom a first signal level to a second signal level, the signal level ofthe first channel at the second level, the communication with theimage-capturing apparatus via a second channel connected via a secondterminal and a third channel connected via a third terminal.
 44. Acontrol method for controlling communication between an image-capturingapparatus and an accessory apparatus in the image-capturing apparatus towhich the accessory apparatus is detachably attachable, the controlmethod comprising: the step of controlling, in response to maintaining,after a signal level of a first channel connected via a first terminalchanges from a first signal level to a second signal level, the signallevel of the first channel at the second level, the communication withthe accessory apparatus via a second channel connected via a secondterminal and a third channel connected via a third terminal.
 45. Anon-transitory storage medium storing a control program as a computerprogram for causing a computer to execute a control method forcontrolling communication between an accessory apparatus and animage-capturing apparatus in the accessory apparatus detachablyattachable to the image-capturing apparatus, the control methodcomprising: the step of controlling, in response to maintaining, after asignal level of a first channel connected via a first terminal changesfrom a first signal level to a second signal level, the signal level ofthe first channel at the second level, the communication with theimage-capturing apparatus via a second channel connected via a secondterminal and a third channel connected via a third terminal.
 46. Anon-transitory storage medium storing a control program as a computerprogram for causing a computer to execute a control method forcontrolling communication between an image-capturing apparatus and anaccessory apparatus in the image-capturing apparatus to which theaccessory apparatus is detachably attachable, the control methodcomprising: the step of controlling, in response to maintaining, after asignal level of a first channel connected via a first terminal changesfrom a first signal level to a second signal level, the signal level ofthe first channel at the second level, the communication with theaccessory apparatus via a second channel connected via a second terminaland a third channel connected via a third terminal.